board: st: stm32mp2: add mmc_get_env_dev()

Use the boot instance to select the correct mmc device identifier,
this patch only to save the environment on eMMC = MMC(1) on
STMicroelectronics boards.

Set the CONFIG_SYS_MMC_ENV_DEV to -1 to select the mmc boot instance
by default.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
2 files changed