pcm: file: add infile read support for mmap mode

pcm: file: add infile read support for mmap mode

mmap_begin callback is used to copy data from input file to mmaped
buffer

guard for corner use of api (multiple mmap_begin calls by user) is
introduced to check if next continuous buffer was already overwritten

buffer is overwritten with input file data only in case of stream capture

Signed-off-by: Adam Miartus <amiartus@de.adit-jv.com>
Reviewed-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>