arm64: dts: r8a7796: Add all SCIF nodes

Add the device nodes for all R-Car H3 SCIF serial ports, incl. clocks
and power domain.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>