[ALSA] oxygen: remove MIDI autodetection

The MIDI bit in the MISC register is set by default and cannot be used
to detect the presence of a MIDI port.  Instead, add a parameter to the
oxygen_pci_probe() function so that model drivers can specify this.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>