Make MTRR min hole alignment 64MB

Make MTRR min hole alignment 64MB

This affects the algorithm when determining when to
transform a range into a larger range with a hole.

It is needed when for when I switch on an 8MB TSEG
and cause the memory maps to go crazy.

Also add header defines for the SMRR.

Change-Id: I1a06ccc28ef139cc79f655a8b19fd3533aca0401
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: http://review.coreboot.org/765
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>