clk: ls1x: Update relationship among all clocks

clk: ls1x: Update relationship among all clocks

- Add clock lookups for APB devices.
 - Update clock relationship to make it more exact and clear.
                                 _____
         _______________________|     |
 OSC ___/                       | MUX |___ XXX CLK
        \___ PLL ___ XXX DIV ___|     |
                                |_____|

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: mturquette@linaro.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8026/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>