ARM: at91/dt: sama5d4: Add pinmux for 8-bit MMC0 bus

Add pinmux for the 4 remaining signals used in 8-bit MMC 0
bus configuration.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Reviewed-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>