image: add ModelNameLimit16

This script returns the model name limited to 16 characters.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

include/image-commands.mk

@@ -3,6 +3,10 @@
 IMAGE_KERNEL = $(word 1,$^)
 IMAGE_ROOTFS = $(word 2,$^)
 
+define ModelNameLimit16
+$(shell expr substr "$(word 2, $(subst _, ,$(1)))" 1 16)
+endef
+
 define rootfs_align
 $(patsubst %-256k,0x40000,$(patsubst %-128k,0x20000,$(patsubst %-64k,0x10000,$(patsubst squashfs%,0x4,$(patsubst root.%,%,$(1))))))
 endef