arm64: dts: ti: k3-j721e-sk: Add missing uart pinmuxes

Rather than depend on the default pinmuxes, explicitly describe the
pinmux

Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20230601183151.1000157-2-nm@ti.com


Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>