src/include: Add PnP/HWM unset_and_set functions

src/include: Add PnP/HWM unset_and_set functions

RMW (read/modify/write) ops on PnP devices has never been so simple.

The semantics also allow the compiler to emit valid warnings if the
input parameters would overflow, which are silenced when the cast is
placed outside of the function.

Change-Id: Ica01211af2a9a00aed98880844a836f6b7957b14
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42134
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>