SBL might change MTRR to enable framebuffer cache. Current code
only handles BSP MTRR programming, and it is necessary to sync
up the MTRR programming for all APs as well. This patch added
a function to sync up MTRRs for all APs.
Please note, this MTRR sync up is a simplified version for SBL
case since SBL will only add new MTRRs for GFX framebuffer.
To do a full generic MTRRs sync up, it is required to flush cache,
reload TLB, etc. And it will come with some performance impacts.
Signed-off-by: Maurice Ma <maurice.ma@intel.com>