uboot-imx

test_avb: Update pymark.buildconfigspec information for the AVB tests

Update the pymark.buildconfigspec to depend on 'cmd_mmc' in addition to
'cmd_avb' for those tests that needs more a more complete MMC
implementation or the "mmc" command.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>