kevin: Save and restore display backlight PWM duty across sysjump
kevin: Save and restore display backlight PWM duty across sysjump

Display backlight going down for an extended period of time is
a major user annoyance, so save the duty prior to sysjump and restore it
upon init.

BUG=chrome-os-partner:56390
BRANCH=None
TEST=On kevin, run "sysjump rw" from recovery screen, verify backlight
goes black for a fraction of a second and comes back to previous level.

Change-Id: I98f12ace9b933874ba9088a790b9efa0941050ed
Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/373621
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec