MIPS: Alchemy: remove old clock support

With the clock framework in place, remove unused functions and bits,
and drop the CLK_IGNORE_UNUSED flag, which is now unneeded.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7473/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>