fix(templates): make nfs-boot.cmd.template architecture-agnostic

The previous template was hardcoded for sunxi arm32 — `zImage`/`bootz`,
`console=tty1 console=ttyS0,115200`, `disp.screen0_output_mode=...`,
`ext4load/fatload mmc 0`. It did not work on arm64 boards (e.g.
rockchip64/helios64) and baked in a 115200 baud that breaks non-standard
UART speeds (helios64 runs at 1500000).

Rewrites the U-Boot hush script to:
- Prefer `Image` + `booti` (arm64), fall back to `zImage` + `bootz` (arm32).
- Load via `${devtype} ${devnum}:${distro_bootpart}` from U-Boot's distro
  bootflow scanner instead of hardcoded `mmc 0`.
- Drop the `console=` overrides — let the kernel resolve the console from
  DTB `/chosen/stdout-path`, keeping `earlycon` for early output.
- Drop sunxi-specific `disp.screen0_output_mode` and legacy `.next`/
  `script.bin` probe paths.

For the full TFTP+NFS netboot flow see the new `netboot` extension; this
template remains the hybrid path where the kernel + DTB live on a local
boot partition and only the rootfs is NFS-mounted.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: iav

config/templates/nfs-boot.cmd.template

@@ -7,27 +7,33 @@
 setenv net_setup "ip=dhcp"
 
 # for static configuration see documentation
-# https://github.com/torvalds/linux/blob/master/Documentation/admin-guide/nfs/nfsroot.rst
+# https://www.kernel.org/doc/Documentation/admin-guide/nfs/nfsroot.rst
 # setenv net_setup "ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns0-ip>:<dns1-ip>"
 
-# you may need to add extra kernel arguments specific to your device
-setenv bootargs "console=tty1 console=ttyS0,115200 root=/dev/nfs ${net_setup} rw rootflags=noatime disp.screen0_output_mode=1920x1080p60 panic=10 consoleblank=0 enforcing=0 loglevel=6"
+# No hardcoded `console=`: kernels resolve the console from the DTB's
+# /chosen/stdout-path. Hardcoding a baud rate here breaks boards whose
+# UART runs at non-115200 speeds (e.g. helios64 @ 1500000).
+setenv bootargs "root=/dev/nfs ${net_setup} rw rootwait earlycon panic=10 loglevel=6"
 
-if test -n ${nfs_root}; then
+if test -n "${nfs_root}"; then
 	setenv bootargs "${bootargs} nfsroot=${nfs_root}"
 fi
 
-if ext4load mmc 0 0x00000000 .next || fatload mmc 0 0x00000000 .next; then
-	ext4load mmc 0 ${fdt_addr_r} /dtb/${fdtfile} || fatload mmc 0 ${fdt_addr_r} /dtb/${fdtfile}
-	ext4load mmc 0 ${kernel_addr_r} zImage || fatload mmc 0 ${kernel_addr_r} zImage
-	ext4load mmc 0 ${ramdisk_addr_r} uInitrd || fatload mmc 0 ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
+# Load kernel + DTB + initrd from the active distro boot partition.
+# devtype/devnum/distro_bootpart are set by U-Boot's bootflow scanner
+# before this script runs.
+setenv boot_dev "${devtype} ${devnum}:${distro_bootpart}"
+
+load ${boot_dev} ${fdt_addr_r} dtb/${fdtfile}
+load ${boot_dev} ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
+
+# Prefer arm64 flat Image (booti); fall back to compressed zImage (bootz).
+if load ${boot_dev} ${kernel_addr_r} Image; then
+	booti ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}
+else
+	load ${boot_dev} ${kernel_addr_r} zImage
 	setenv fdt_high ffffffff
 	bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}
-else
-	ext4load mmc 0 ${fdt_addr_r} script.bin || fatload mmc 0 ${fdt_addr_r} script.bin
-	ext4load mmc 0 ${kernel_addr_r} zImage || fatload mmc 0 ${kernel_addr_r} zImage
-	ext4load mmc 0 ${ramdisk_addr_r} uInitrd || fatload mmc 0 ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
-	bootz ${kernel_addr_r} ${ramdisk_addr_r}
 fi
 
 # Recompile with: