clk: Add Microchip PolarFire SoC clock driver

Add clock driver code for the Microchip PolarFire SoC. This driver
handles reset and clock control of the Microchip PolarFire SoC device.

Signed-off-by: Padmarao Begari <padmarao.begari@microchip.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Tested-by: Bin Meng <bin.meng@windriver.com>