arm64: dts: ti: am654-base-board: Add pinmux for main uart0

Add pinmux for main uart0 that is serves as console on AM654 EVM

Signed-off-by: Vignesh R <vigneshr@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>