clk: Loongson1: Refactor Loongson1 clock

Factor out the common functions into loongson1/clk.c
to support both Loongson1B and Loongson1C. And, put
the rest into loongson1/clk-loongson1b.c.

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>