ARM: stm32: Add dh_update_sd_to_emmc to STM32MP15xx DHCOR

Add script which installs U-Boot binaries from SD card to eMMC
and makes the eMMC bootable.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>