util/cbmem: handle larger than 1MiB mappings for console

In some cases the cbmem console can be larger than the default
mapping size of 1MiB. Therefore, add the ability to do a mapping
that is larger than the default mapping using map_memory_size().
The console printing code will unconditionally map the console based
on the size it finds in the cbmem entry.

Change-Id: I016420576b9523ce81195160ae86ad16952b761c
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5440
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>