ARM: shmobile: r8a7779: Use MSTP for SCIF clocks

Hook up MSTP clocks to SCIF devices on r8a7779 to allow
clock gating to work as expected.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>