dt-bindings: clock: Add Loongson-2K expand clock index

In the new Loongson-2K family of SoCs, more clock indexes are needed,
such as clock gates.
The patch adds these clock indexes

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/76844e0e4dae290425f7c8025f7f36810cb3a3a8.1712731524.git.zhoubinbin@loongson.cn


Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>