V4L/DVB (3214): Calculate the saa7115 AMCLK regs instead of using fixed values

- Calculate the audio master clock registers from the actual
frequencies. This simplifies the code and it also prepares
for adding CGC2 support.
- VIDIOC_INT_AUDIO_CLOCK_FREQ now receives an u32 instead of
an enum. It is more generic and actually easier to implement.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@brturbo.com.br>