zephyr: emul: get emul_port with DEVICE_DT_GET
zephyr: emul: get emul_port with DEVICE_DT_GET

Change ap_power test to get the gpio port using the nodelabel instead of
the label property. This works with upstream, where the label property
is being removed.

BRANCH=none
BUG=none
TEST=zmake testall

Cq-Depend: chromium:3813331
Signed-off-by: Fabio Baltieri <1c55e39c05d9ab42261288cf330256b2af6ba179@google.com>
Change-Id: I4a2752c358aac8e4a8f2e59c55982f2386b30485
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3811112
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