ARM: shmobile: r8a7778 SCIF support

Add SCIF serial port support to the r8a7778 SoC by
adding platform devices together with clock bindings.
DT device description is excluded at this point since
such bindings are still under development.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>