Makefile: Only compile vesa for archs that need it

The vesa framebuffer is only used by architectures that explicitly
require it (i.e. x86). Compile it out for architectures not using it, as
its current implementation might not work for them.
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Makefile

@@ -98,7 +98,6 @@ OBJS	+= util/read-write.o
 OBJS	+= util/util.o
 OBJS	+= virtio/9p.o
 OBJS	+= virtio/9p-pdu.o
-OBJS	+= hw/vesa.o
 OBJS	+= hw/pci-shmem.o
 OBJS	+= kvm-ipc.o
 OBJS	+= builtin-sandbox.o
@@ -223,6 +222,8 @@ else
 endif
 
 ifeq (y,$(ARCH_HAS_FRAMEBUFFER))
+	OBJS	+= hw/vesa.o
+
 	CFLAGS_GTK3 := $(shell pkg-config --cflags gtk+-3.0 2>/dev/null)
 	LDFLAGS_GTK3 := $(shell pkg-config --libs gtk+-3.0 2>/dev/null)
 	ifeq ($(call try-build,$(SOURCE_GTK3),$(CFLAGS) $(CFLAGS_GTK3),$(LDFLAGS) $(LDFLAGS_GTK3)),y)