clk: clk-loongson2: Refactor driver for adding new platforms

The driver only supported loongson-2K1000 at first, but the clock
structure of loongson-2K0500 and loongson-2K2000 are actually similar,
and I tried to refactor the whole driver to adjust to the addition of
the new platform.

Briefly, I have divided all clocks into three categories according to
their properties and their parent clocks: Independent PLLs, clocks based
on frequency scales, and clock dividers.
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Link: https://lore.kernel.org/r/fb020d1ca19e6f4cdcc95c87b2748869ca76b8ec.1712731524.git.zhoubinbin@loongson.cnAcked-by: Huacai Chen <chenhuacai@loongson.cn>
[sboyd@kernel.org: Drop clk.h include]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>