[ALSA] Fix and clean-up of vxpocket driver

Documentation,PCMCIA Kconfig,Digigram VX Pocket driver
- Fixed Oops with request_firmware()
- Detect the card type in runtime (vxpoocket v2 or 440)
- snd-vxp440 driver is merged to snd-vxpocket
- Clean up the code

Signed-off-by: Takashi Iwai <tiwai@suse.de>