arm64: dts: ti: k3-j721e-main: Add dts nodes for EHRPWMs

Add dts nodes for 6 EHRPWM instances on SoC. Disable EHRPWM nodes in the
dtsi files and only enable the ones that are actually pinned out on a
given board.

Includes a minor formatting fixup for the serdes node to line up the
nodes appropriately.

Signed-off-by: Vijay Pothukuchi <vijayp@ti.com>
Signed-off-by: Rahul T R <r-ravikumar@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20221107070009.11500-2-r-ravikumar@ti.com