cr50: init rbox before the board init is invoked
cr50: init rbox before the board init is invoked

Board initialization function configures certain RBOX registers, but
RBOX initialization runs at the same priority as board initialization,
and as such is not guaranteed to run in time.

Reducing RBOX initialization priority guarantees that RBOX is
initialized by the time board init function needs to access it.

BRANCH=none
BUG=chrome-os-partner:49959
TEST=the AP_WP_L signal now reports the expected value:
   > gpioget AP_WP_L
     1  AP_WP_L
   >

Change-Id: I9c29451a08fc47d3409031bda1a936de243c0c70
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/358169
Tested-by: Brian Norris <67059238af8e1945c40edb274ce1d51ba595dbf3@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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