Fix default DMIC gain on AMD PDM drivers

Fix default DMIC gain on AMD PDM drivers

Merge series from Mario Limonciello <mario.limonciello@amd.com>:

It's been reported that a number of laptops have a low volume
level from the digital microphone compared to Windows.

AMD offers a register that can adjust the gain for PDM which is not
configured at maximum gain by default.

To fix this change the default for all 3 drivers to raise the gain
but also offer a module parameter. The module parameter can be used
for debugging if the gain is too high on a given laptop.

This is intentionally split into multiple patches for default and
parameter so that if the default really does behave better universally
we can bring it back to stable too later.