grub2: Add GRUB_MKIMAGE_OPTS for configurable grub-mkimage options

Introduce the GRUB_MKIMAGE_OPTS variable to allow additional options
to be passed to grub-mkimage, making its behavior more configurable.
(for example, this allows disabling shim lock when necessary).

Update do_mkimage to use ${GRUB_MKIMAGE_OPTS}. This change reduce the
need for hardcoded modifications and makes future adjustments easier.

(From OE-Core rev: a6147adefcba7aae3f4eb8ed76d6a94315cafe61)

Signed-off-by: Valeria Petrov <valeria.petrov@spinetix.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-bsp/grub/grub-efi_2.12.bb

@@ -46,6 +46,9 @@ inherit deploy
 CACHED_CONFIGUREVARS += "ac_cv_path_HELP2MAN="
 EXTRA_OECONF += "--enable-efiemu=no"
 
+# Define GRUB_MKIMAGE_OPTS variable for additional grub-mkimage options (e.g., disabling shim lock)
+GRUB_MKIMAGE_OPTS ?= ""
+
 do_mkimage() {
 	cd ${B}
 
@@ -62,7 +65,7 @@ do_mkimage() {
 	# built in cfg file provided via this recipe
 	grub-mkimage -v -c ${UNPACKDIR}/cfg -p ${EFIDIR} -d ./grub-core/ \
 	               -O ${GRUB_TARGET}-efi -o ./${GRUB_IMAGE_PREFIX}${GRUB_IMAGE} \
-	               ${GRUB_MKIMAGE_MODULES}
+	               ${GRUB_MKIMAGE_OPTS} ${GRUB_MKIMAGE_MODULES}
 }
 
 addtask mkimage before do_install after do_compile