baytrail: romstage: Add function to check SW WP status for vboot

Implement vboot_get_sw_write_protect, which returns the FW SPI ROM SW WP
status.

BUG=chrome-os-partner:26777
TEST=Manual on Rambi with all patches in sequence:
`crossystem sw_wpsw_boot` prints 0
`flashrom --wp-enable` + reboot
`crossystem sw_wpsw_boot` prints 1
BRANCH=Rambi

Original-Change-Id: I5da35c1b2d25b8679bf0084af65d08de224387f8
Original-Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/190097
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
(cherry picked from commit 5bba447654417c42952c49542ed047b4867d04d1)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I739cbb8fca5f02462cf78c81f9b364aabfd3fe86
Reviewed-on: http://review.coreboot.org/7211
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
5 files changed