ALSA: core: Add continuous and vmalloc mmap ops

The mmap of continuous pages and vmalloc'ed pages are relatively
easily done in a shot with the existing helper functions.
Implement the mmap ops for those types, so that the mmap works without
relying on the page fault handling.

Link: https://lore.kernel.org/r/20210609162551.7842-6-tiwai@suse.de


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