zephyr: flash: it8xxx2: lower cros_flash priority
zephyr: flash: it8xxx2: lower cros_flash priority

CL:3398577 changed driver layer priority, so cros_flash_it8xxx2
should be lowered.

BUG=none
BRANCH=none
TEST=Boot normally on it8xxx2_evb and hayato.
zmake -lDEBUG configure -b zephyr/projects/it8xxx2_evb/
zmake -lDEBUG configure -b zephyr/projects/asurada/hayato/

Signed-off-by: Tim Lin <38846f7070d5770410e9ef8b439c72e7b53a72c5@ite.corp-partner.google.com>
Change-Id: I3509508c85d2fd55b74596c87e27d1bf4044e50d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3400761
Reviewed-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>

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