Add guard for UMA globals

We no longer need these globally. Guard them so we get to declare
static replacements at few locations until complete removal.

Change-Id: Ie33e2a680fc9bbb7e28c8fbe17e5181e626736a5
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5718
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/include/device/device.h

@@ -131,9 +131,11 @@ extern struct bus	*free_links;
 
 extern const char mainboard_name[];
 
+#if CONFIG_GFXUMA
 /* IGD UMA memory */
 extern uint64_t uma_memory_base;
 extern uint64_t uma_memory_size;
+#endif
 
 /* Generic device interface functions */
 device_t alloc_dev(struct bus *parent, struct device_path *path);