vboot: introduce get_gbb_flags.sh

introduce get_gbb_flags.sh command to make automatic annotation
of power measurements easier.

Also, fix issue where declaring local variables on same line
as executing a command would obfuscate error code, thus not
triggering set -c and continuing execution.
https://github.com/koalaman/shellcheck/wiki/SC2155

Usage:
$ /usr/share/vboot/bin/get_gbb_flags.sh
[...]
ChromeOS GBB set flags: 0x00000329.

$ /usr/share/vboot/bin/get_gbb_flags.sh -e
[...]
ChromeOS GBB set flags: 0x00000329.
ChromeOS GBB set flags listed:
GBB_FLAG_DEV_SCREEN_SHORT_DELAY
GBB_FLAG_FORCE_DEV_SWITCH_ON
GBB_FLAG_DISABLE_FW_ROLLBACK_CHECK
GBB_FLAG_FAFT_KEY_OVERIDE
GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC

BUG=chromium:760267
BRANCH=none
TEST=manual
emerge-soraka vboot_reference
cros deploy <IP> vboot_reference
(on DUT)
/usr/share/vboot/bin/get_gbb_flags.sh -e
<same output as above>

Change-Id: Idb3b993706c03e7f2831eed2cef12a04b9469fea
4 files changed