ARM: dts: am574x-idk: Add pinmuxes for mmc1 and mmc2

Sync with kernel dts by adding pinmuxes for mmc1 and mmc2. This fixes an
issue where mmc2 (eMMC) was coming up in HS52 mode instead of the
highest DDR52 mode.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>