clk: Add common clock driver for BM1880 SoC

Add common clock driver for Bitmain BM1880 SoC. The clock controller on
BM1880 has supplies clocks to all peripherals in the form of gate clocks
and composite clocks (fixed factor + gate).

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lkml.kernel.org/r/20191115162901.17456-7-manivannan.sadhasivam@linaro.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>