ARM: shmobile: r8a73a4: add a DMAC platform device and clock for it

Add a DMAC platform device and clock definitions for it on r8a73a4.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>