grub: remove GRUB_SUPPORTED_ARCH

grub can already only be selected for x86 and x86_64. No need to check
again for this in grub.mk.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

boot/grub/grub.mk

@@ -1,20 +1,3 @@
-GRUB_SUPPORTED_ARCH=n
-ifeq ($(ARCH),i386)
-GRUB_SUPPORTED_ARCH=y
-endif
-ifeq ($(ARCH),i486)
-GRUB_SUPPORTED_ARCH=y
-endif
-ifeq ($(ARCH),i586)
-GRUB_SUPPORTED_ARCH=y
-endif
-ifeq ($(ARCH),i686)
-GRUB_SUPPORTED_ARCH=y
-endif
-ifeq ($(ARCH),x86_64)
-GRUB_SUPPORTED_ARCH=y
-endif
-ifeq ($(GRUB_SUPPORTED_ARCH),y)
 #############################################################
 #
 # grub
@@ -125,8 +108,6 @@ grub-clean:
 grub-dirclean:
 	rm -rf $(GRUB_DIR)
 
-endif
-
 #############################################################
 #
 # Toplevel Makefile options