zephyr: Restore legacy GPIO tests
zephyr: Restore legacy GPIO tests

To ensure full coverage, restore tests of
legacy GPIO API.

BUG=b:219368141
TEST=zmake configure --test test/drivers
BRANCH=none

Signed-off-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Change-Id: I819d63612b12054bc12acc89e851e22ac1eb0833
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3460763
Reviewed-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>

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