added support for BRD4350A, BRD4351A and BRD2709A

[Sarthak-Shaha]

Problem / Feature

Need to add support files for BRD4150A

Change overview

Added autogen and config files for BRD4350A Made modifications by comparing it with BRD4187C and BRD4116A

Note: need to remove comments from code

Testing

Able to build light-switch thread app

[mkardous-silabs]

i think there might be a typo in the tittle