Makefile: Correct logic for DM_SCSI + unconverted drivers check

Makefile: Correct logic for DM_SCSI + unconverted drivers check

When checking for boards that are enabling a SATA driver that isn't
converted to DM yet we need to be sure to not also trip over boards that
do set CONFIG_AHCI & CONFIG_BLK by itself, as that is not a bug.

This was detected when converting the Armada XP SATA driver sata_mv.c
to DM with AHCI & BLK support. This warning is still printed without
this patch applied here.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>