helpers: Add GENMASK macro

The GENMASK is defined in multiple files (with various names such as
MASKBIT), which sets certain consecutive bits to 1 and leaves the others
to 0. To avoid duplicate macros, add GENMASK macro to helpers.h.

GENMASK(high, low) sets bits from `high` to `low` (inclusive) to 1. For
example, GENMASK(39, 21) gives us the 64-bit vector 0x000000ffffe00000.

Remove duplicate macro definitions. Also utilize GENMASK for _BF_MASK in
mmio.h.

BUG=none
TEST=make tests/commonlib/bsd/helpers-test
TEST=emerge-cherry coreboot
BRANCH=none

Change-Id: If2e7c4827d8a7d27688534593b556a72f16f0c2b
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56543
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

0 files changed, 0 insertions, 0 deletions