clk: ingenic: Allow drivers to be built with COMPILE_TEST

We don't need the MIPS architecture or even a MIPS compiler to compile
test these drivers. Let's add a COMPILE_TEST possibility on the
menuconfig here so that we can build these drivers on more
configurations.

Cc: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lkml.kernel.org/r/20191114001925.159276-1-sboyd@kernel.org
Reviewed-by: Paul Cercueil <paul@crapouillou.net>