clk: sirf: re-arch to make the codes support both prima2 and atlas6

sirfprima2 and sirfatlas6 are two different SoCs in CSR SiRF series. for
prima2 and atlas6, there are many shared clocks but there are still
some different register layout and hardware clocks, then result in
different clock table.

here we re-arch the driver to
1. clk-common.c provides common clocks for prima2 and atlas6,
2. clk-prima2.h describles registers of prima2 and clk-prima2.c provides
prima2 specific clocks and clock table.
3. clk-atlas6.h describles registers of atlas6 and clk-atlas6.c provides
atlas6 specific clocks and clock table.
4. clk.h and clk.c expose external interfaces and provide uniform entry
for both prima2 and atlas6.

so both prima2 and atlas6 will get support by drivers/clk/sirf.

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Rongjun Ying <Rongjun.Ying@csr.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>