nb/intel/i945: Add a common function to compute TSEG size

This adds a common function to decode the TSEG size from the ESMRAM
register. This will come in handy when SMM in TSEG is implemented.

This function is used both in romstage and in ramstage.

Change-Id: I4e163598752fb6cd036aec229fce439ebad74def
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/23448
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
3 files changed