mb/google/gale to nyan_blaze: Rename Makefiles from .inc to .mk

The .inc suffix is confusing to various tools as it's not specific to
Makefiles. This means that editors don't recognize the files, and don't
open them with highlighting and any other specific editor functionality.

This issue is also seen in the release notes generation script where
Makefiles get renamed before running cloc.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I92f8bd7e1c9fc6e4120fb94c2299a266304e19de
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80107
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/myst/Makefile.mk

@@ -28,7 +28,7 @@ APCB_SOURCES = $(MAINBOARD_BLOBS_DIR)/$(APCB_NAME).bin
 # Add the below section back in after the apcbtool is updated to handle the
 # Phoenix APCB SPD configuration.
 
-ifneq ($(wildcard $(src)/mainboard/$(MAINBOARDDIR)/variants/$(VARIANT_DIR)/memory/Makefile.inc),)
+ifneq ($(wildcard $(src)/mainboard/$(MAINBOARDDIR)/variants/$(VARIANT_DIR)/memory/Makefile.mk),)
 
 LIB_SPD_DEPS = $(SPD_SOURCES)