The Renesas Salvator-X development board can be equipped with either an
R-Car H3 or M3-W SiP, which are pin-compatible.  Both boards use
different DTBs.

Reduce duplication by extracting common Salvator-X board support into
its own .dtsi file.  References to SoC-specific clocks are handled
through cpp definitions.  Sort device nodes while at it.

For boards with an R-Car H3 SiP, there are no functional changes.

For boards with an R-Car M3-W SiP, the following new devices are now
described in DT:
  - External audio, CAN, and PCIe clocks,
  - USB Vbus regulator,
  - CS2000 clock generator,
  - AK4613 Audio Codec,
  - VGA.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>