media: davinci: allow building isif code

The only reason why this driver doesn't build with COMPILE_TEST
is because it includes mach/mux.h. It turns that none of the
macros defined there are used.

So, get rid of it, in order to allow it to build with
COMPILE_TEST.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>