uboot-phytec

stm32mp1: cosmetic cleanup Kconfig

Cosmetic cleanup in mach-stm32mp Kconfig
- remove duplicated SPL_DRIVERS_MISC_SUPPORT
- update help for TARGET_STM32MP1
- set value for NR_DRAM_BANKS
- remove one comment as DEBUG_UART is deactivated by default
- include board Kconfig at the end of the file

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>