ALSA: asihpi: Replace tasklet with threaded irq

The tasklet is an old API that should be deprecated, usually can be
converted to another decent API.  In ASIHPI driver, a tasklet is
still used for offloading the PCM IRQ handling.  It can be achieved
gracefully with a threaded IRQ, too.

This patch replaces the tasklet usage in asihpi driver with a threaded
IRQ.  It also simplified some call patterns.

Link: https://lore.kernel.org/r/20200903104131.21097-10-tiwai@suse.de


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