sata: Only support BLK

No boards currently use SATA without BLK:

   ./tools/moveconfig.py -f SATA ~BLK
   0 matches

Make SATA depend on BLK to avoid any future confusion. Drop the dead code.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>