ARM: dts: k2g-evm: Add pinmuxing for UART0

Avoid depending on the bootloader or the ROM for configuring the pinmux by
explicitly setting the pinmux here.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>