configs: Enable CONFIG_DM_SCSI in am57xx_hs_evm_usb

This should have already been enabled but was missed when converting the
base platform defconfig, fix this here.

Fixes: 3c5aa6ca ("configs: Enable CONFIG_BLK in am57xx_evm and am57xx_hs_evm")
Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>