link: If a required power rail drops, shut down
link: If a required power rail drops, shut down

This protects the system from ending up in a weird state if one of the
rails fails to come up, or shuts down after coming up.

BUG=chrome-os-partner:17774
BRANCH=link
TEST=manual

- Boot system
- From EC console: gpioset enable_1_5v_ddr 0
- System shuts down; EC console prints "x86 power lost input"
- Press power button; system turns back on
- From EC console: gpioset enable_vs 0
- System shuts down; EC console prints "x86 power lost input"
- Press power button; system turns back on
- Suspend system
- From EC console: gpioset enable_1_5v_ddr 0
- System shuts down; EC console prints "x86 power lost input"
- Press power button; system turns back on

Change-Id: I8ae1630deb4001716b8dfd89d7dec7300cddb5ae
Signed-off-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/43097
Reviewed-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

alterapraxisptyltd/chromium-ec,alterapraxisptyltd/chromium-ec,fourier49/BZ_DEV_EC,fourier49/BIZ_EC,fourier49/BZ_DEV_EC,gelraen/cros-ec,coreboot/chrome-ec,fourier49/BIZ_EC,md5555/ec,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,fourier49/BZ_DEV_EC,md5555/ec,thehobn/ec,eatbyte/chromium-ec,alterapraxisptyltd/chromium-ec,eatbyte/chromium-ec,md5555/ec,alterapraxisptyltd/chromium-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,thehobn/ec,coreboot/chrome-ec,longsleep/ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,longsleep/ec,coreboot/chrome-ec,gelraen/cros-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,mtk09422/chromiumos-platform-ec,mtk09422/chromiumos-platform-ec,longsleep/ec,mtk09422/chromiumos-platform-ec,mtk09422/chromiumos-platform-ec,akappy7/ChromeOS_EC_LED_Diagnostics,gelraen/cros-ec,coreboot/chrome-ec,eatbyte/chromium-ec,gelraen/cros-ec,thehobn/ec,fourier49/BIZ_EC,thehobn/ec