zephyr test: Test VBUS sink enable/disable
zephyr test: Test VBUS sink enable/disable

Verify register values after enabling VBUS sink and after disabling it.

BUG=b:190519131
TEST=zmake congfigure --test zephyr/test/drivers
BRANCH=none

Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Change-Id: Ibfb17252d3c31131101a6ba5682584148f747164
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3318726
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

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