ALSA: core: Move mmap handler into memalloc ops

This patch moves the mmap handling code into the common memalloc
handler.  It allows us to reduce the memory-type specific code in PCM
code gracefully.

Link: https://lore.kernel.org/r/20210609162551.7842-5-tiwai@suse.de


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