spi: Add function to read flash status register

Add a function that allows reading of the status register
from the SPI chip.  This can be used to determine whether
write protection is enabled on the chip.

BUG=chrome-os-partner:35209
BRANCH=haswell
TEST=build and boot on peppy

Cq-Depend: chromium:2044929
Change-Id: I2541b22c51e43f7b7542ee0f48618cf411976a98
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/240702
Reviewed-by: Shawn N <shawnn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/coreboot/+/2044928
Reviewed-by: Dossym Nurmukhanov <dossym@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Tested-by: Dossym Nurmukhanov <dossym@chromium.org>
Commit-Queue: Dossym Nurmukhanov <dossym@chromium.org>
8 files changed