lenovo/t520: Use native raminit over MRC blob

Native raminit for sandy/ivybridge was introduced in:

7686a56 sandy/ivybridge: Native raminit.

An additional current level is needed.

Change-Id: Ied73d168045c25d37afa5d9d7073de7f9c6435c7
Signed-off-by: Nicolas Reinecke <nr@das-labor.org>
Signed-off-by: Philipp Deppenwiese <zaolin@das-labor.org>
Reviewed-on: http://review.coreboot.org/7098
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Tested-by: build bot (Jenkins)