imx: mx6: Implement mmc_get_env_part

commit 216d286c7e3d3d83d4d8ccaf0415192e1b1040c0 [imx: mx6: implement
mmc_get_env_dev] introduced selection of the environment device according
to the boot device when booting from SD/MMC.

Extend this functionality for also selecting the device partition.

Signed-off-by: Soeren Moch <smoch@web.de>
1 file changed