configs: stm32f746-disco: enable MMC related flags

STM32F469-disco embeds an arm_pl180 mmc IP, so
enable CMD_MMC, DM_MMC and ARM_PL180_MMCI flags.

Also enables all filesystem command related flags :
  _ CMD_EXT2
  _ CMD_EXT4
  _ CMD_FAT
  _ CMD_FS_GENERIC
  _ CMD_GPT
  _ CMD_BOOTZ

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>