mvebu: helios4 edge → 6.18 LTS, restore orphaned patches

Commit 2f852e6 bumped mvebu edge KERNEL_MAJOR_MINOR from 6.12 to 6.15
but did not rename patch/kernel/archive/mvebu-6.12/, so KERNELPATCHDIR
pointed to a non-existent directory and all helios4-specific kernel
patches (GPIO wake, Wake-on-LAN, atheros regd, DMA, SPI-flash) were
silently skipped.

6.15 is not an LTS kernel; 6.18 is. Bump only helios4 to 6.18 (LTS, EOL
2028-12), keeping the rest of the mvebu family at 6.15 until their
maintainers verify the upgrade on their own boards.

Rename the archive directory to mvebu-6.18 so the patches apply again,
verified by a full kernel build against 6.18.23.

Author: iav

config/sources/families/mvebu.conf

@@ -31,7 +31,11 @@ case $BRANCH in
 
 	edge)
 
-		declare -g KERNEL_MAJOR_MINOR="6.15" # Major and minor versions of this kernel.
+		if [[ $BOARD == helios4 ]]; then
+			declare -g KERNEL_MAJOR_MINOR="6.18" # helios4: 6.18 LTS, restore orphaned mvebu patches
+		else
+			declare -g KERNEL_MAJOR_MINOR="6.15" # Major and minor versions of this kernel.
+		fi
 		;;
 
 esac