npcx: adc: Properly wait for conversion interrupt
npcx: adc: Properly wait for conversion interrupt

Certain tasks (eg. chipset) may be woken directly by other tasks /
unrelated interrupts. Add an explicit wake event for ADC conversion done
so that we're not mistakenly woken.

BUG=chrome-os-partner:54971
BRANCH=None
TEST=Manual on kevin rev5, run "reboot ap-off" then "sysjump rw", verify
console isn't spammed with GPIO warning message due to ADC failure to
read board version.

Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

Change-Id: I5477e11c2b434e4b350d81393f4463eea1a91e7c
Reviewed-on: https://chromium-review.googlesource.com/366943
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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