[ALSA] emu10k1: Add module option uint subsystem.

EMU10K1/EMU10K2 driver
It allows the user to force the snd-emu10k1 module to think the user
has a particular sound card. Useful if their particular sound card
is not yet recognised.

Signed-off-by: James Courtier-Dutton <James@superbug.co.uk>