dm: add dvfs uclass and wide temperature dvfs support

- add dvfs uclass;
- add dvfs command;
- add a simple wide temperature dvfs driver.

About wide temperature dvfs driver policy, see description

dm: add dvfs uclass and wide temperature dvfs support

- add dvfs uclass;
- add dvfs command;
- add a simple wide temperature dvfs driver.

About wide temperature dvfs driver policy, see description in:
drivers/power/dvfs/rockchip_wtemp_dvfs.c

Change-Id: I36a8de6e47f8375bf1795b794c77d96b4571a361
Signed-off-by: Joseph Chen <chenjh@rock-chips.com>

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