util: 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: I434940ebb46853980596f7ad55d27a62c90280fa
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80123
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/Makefile.mk b/Makefile.mk
index 87c6bcb..f7b98c7 100644
--- a/Makefile.mk
+++ b/Makefile.mk
@@ -768,7 +768,7 @@
 install-git-commit-clangfmt:
 	cp util/scripts/prepare-commit-msg.clang-format .git/hooks/prepare-commit-msg
 
-include util/crossgcc/Makefile.inc
+include util/crossgcc/Makefile.mk
 
 .PHONY: tools
 tools: $(objutil)/kconfig/conf $(objutil)/kconfig/toada $(CBFSTOOL) $(objutil)/cbfstool/cbfs-compression-tool $(FMAPTOOL) $(RMODTOOL) $(IFWITOOL) $(objutil)/nvramtool/nvramtool $(objutil)/sconfig/sconfig $(IFDTOOL) $(CBOOTIMAGE) $(AMDFWTOOL) $(AMDCOMPRESS) $(FUTILITY) $(BINCFG) $(IFITTOOL) $(objutil)/supermicro/smcbiosinfo $(CSE_FPT) $(CSE_SERGER) $(AMDFWREAD)