PM / devfreq: exynos: Add generic exynos bus frequency driver

PM / devfreq: exynos: Add generic exynos bus frequency driver

This patch adds the generic exynos bus frequency driver for AMBA AXI bus
of sub-blocks in exynos SoC with DEVFREQ framework. The Samsung Exynos SoC
have the common architecture for bus between DRAM and sub-blocks in SoC.
This driver can support the generic bus frequency driver for Exynos SoCs.

In devicetree, Each bus block has a bus clock, regulator, operation-point
and devfreq-event devices which measure the utilization of each bus block.

Signed-off-by: Chanwoo Choi <[email protected]>
[m.reichl and linux.amoon: Tested it on exynos4412-odroidu3 board]
Tested-by: Markus Reichl <[email protected]>
Tested-by: Anand Moon <[email protected]>
Signed-off-by: MyungJoo Ham <[email protected]>
Acked-by: Krzysztof Kozlowski <[email protected]>