Define global uma_memory variables

Use of the uma_memory_base and _size variables is very scattered.
Implementation of setup_uma_memory() will appear in each northbridge.

It should be possible to do this setup entirely in northbridge
code and get rid of the globals in a follow-up.

Change-Id: I07ccd98c55a6bcaa8294ad9704b88d7afb341456
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/1204
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/mainboard/amd/south_station/mainboard.c

@@ -28,7 +28,6 @@
 #include "SBPLATFORM.h" 	/* Platfrom Specific Definitions */
 #include "chip.h"
 
-uint64_t uma_memory_base, uma_memory_size;
 
 void set_pcie_reset(void);
 void set_pcie_dereset(void);