soc/amd: Throw an error if FWM_POSITION_INDEX is empty

The empty string causes an undetectable build error.

Filter out the board which doesn't define this variable.
A great odds that the reason is the board doesn't set a
valid ROM size.

Change-Id: Iade1961460285acdec245c553c7b84014c30c267
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49855
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

0 files changed, 0 insertions, 0 deletions