nehalem: Make UMA size configurable in CMOS.

All modes tested on X201.

Change-Id: I23df81523196ea3f5fdb10eb04f4496c00aaeb9f
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/6481
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>