ARM: shmobile: r8a73a4: implement CPU clock scaling for CPUFreq

This patch adds support for the Z-clock on r8a73a4 SoCs, which is driving
the Cortex A15 core, and a "cpufreq-cpu0" platform device. Adding an
"operating-points" property to the CPU0 DT node and a regulator, this
patch allows platforms to use the generic cpufreq-cpu0 driver to use
SoC's DVFS capabilities.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>