MLK-21852 imx: Update runtime SD/MMC boot env device and env variables

MLK-21852 imx: Update runtime SD/MMC boot env device and env variables

Since we enabled MMC alias, the USDHC index in u-boot is the usdhc port.
So we don't need to convert them for kernel and u-boot env device.

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit 8fd6e14f5c1598684bc08a7917f89cd94e988d8f)
(cherry picked from commit 96bc8f724159a3a9e2ba9f605b84f53534bc3e1f)
(cherry picked from commit 83a2f62405d0aa3b1fe7140e320a1b297d6b4883)
(cherry picked from commit 733b8ad42e057bd025cd97a570ecbcb2ebc4191c)