ALSA: ctxfi - Add PM support

Added the suspend/resume support to ctxfi driver.

The team tested on the following seems ok:
  AMD Athlon 64 3500+ / ASUS A8N-E / 512MB DDR ATI / Radeon X1300
  20k1 & 20k2 cards

Signed-off-by: Wai Yew CHAY <wychay@ctl.creative.com>
Singed-off-by: Ryan RICHARDS <ryan_richards@creativelabs.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>