MIPS: Alchemy: irda: use clk framework

Test the existence of the irda_clk clock object, use it to en/dis-
able it when date is being transferred.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7470/


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