hatch: refactor gpio table into baseboard, allow empty SPDs

Each variant needed to define variant_early_gpio_table(), even if
it didn't need to make any changes. Added a __weak version of the
function into baseboard/gpio.c.

Certain upcoming Hatch variants will not use SPD files. Allow
SPD_SOURCES in spd/Makefile.inc to be empty.

BUG=None
BRANCH=None
TEST=Build coreboot and see that it builds without error

Change-Id: Ie946cfd7c071824168faa38fd53bd338a5a451e1
Signed-off-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36068
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

0 files changed, 0 insertions, 0 deletions