Currently the info in /proc/interrupts doesn't allow to figure out which
interrupt belongs to which card (HDMI, PCH, ..).
Therefore add card details to the interrupt description.
With the patch the info in /proc/interrupts looks like this:

PCI-MSI 442368-edge      snd_hda_intel:card1
PCI-MSI 49152-edge      snd_hda_intel:card0

NOTE: this patch adds the new irq_descr field snd_card struct that is
filled automatically at a card object creation.  This can be used
generically for other drivers as well.  The changes for others will
follow later -- tiwai

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>