Add common functions to manipulate PMBASE IO window.
TODO:
* Use the new functions to manipulate register in PMBASE.
* Get rid of duplicated get_pmbase()
Change-Id: I3b454434ade560fb056b1fc0afe9541df93e14dd
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/27278
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
