[hack] si476x: Add support for powering 4735 chip up

Add a terrible hack to support powering the chip up. All initial values
are hardcoded instead of being retrieved from DT, so this would have
to be fixed.
[hack] si476x: Implement misc. config routines

implement misc. config routines for configuring pinmux(a stub in case
of si4735) and device version information retrieval.
[will break the build] Backup commit to save my refactoring changes