arm64 dts ti k3 j721e: Changes for enabling HW PWM on J721e SK platform

The following has been done in this commit:
1) Add new nodes definitions for enabling all 6 EHRPWM instances
2) Add rules to disable all the instances for non SK platforms
3) Add rules to enable instances 2 and 3 for the SK platform
4) Add mux settings for enabling channel A from instances 2 and 3
   for the RPi extension header on the SK platform