MLK-17621-2 mmc: add feature of setting slot index via devicetree alias

MLK-17621-2 mmc: add feature of setting slot index via devicetree alias

Add feature of setting slot index via devicetree alias, to hard code the
mmc/sd root device.

The patch requires additional alias_id fix or it won't work.

Note: minor device number keep independent with this device alias.

Refer to the commit 35928d6c6a76 ("mmc: Allow setting slot index via
devicetree alias").

Acked-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>