npcx: rtc: Write RTC reg twice to ensure non-volatility
npcx: rtc: Write RTC reg twice to ensure non-volatility

TTC must be written twice, otherwise the value will be lost on EC reset,
even if VBAT stays stable.

BUG=chrome-os-partner:57010
BRANCH=None
TEST=On kevin, run 'rtc set 55555' then trigger cold reset through
servo. Run 'rtc' on subsequent boot and verify timing ticks did not
reset to zero.

Change-Id: If05b698e75eece5f8879a109b98886b547eb71a4
Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/382654
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