ARM: shmobile: r8a7779: Reference clocks

Reference clocks using a "clocks" property in all nodes corresponding to
devices that require a clock.

Based on work by Laurent Pinchart for the r8a7790 and r8a7791 SoC.

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>