zinger: update OVP latch condition
zinger: update OVP latch condition

The Over Voltage Protection was de-activated when the output is disabled
to avoid false positive when doing a down voltage transition,
but as a side effect, we might reset the OVP while the fault is still
present since the OVP first disables the output.
So, we want to keep testing the OVP fault condition if there is a
pre-existing fault.

Also add a hysteris and ensure we recover from OVP only when we go under
the new threshold.

Signed-off-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

BRANCH=none
BUG=chrome-os-partner:28331
TEST=trigger an OVP using a voltage source and see the output is not
re-enabled until we shutdown the voltage source.

Change-Id: Idef3f630c3cfeb301e62f1e75c2a424b56bc98dd
Reviewed-on: https://chromium-review.googlesource.com/206185
Reviewed-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Commit-Queue: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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