ALSA: core: Add memory copy helpers between iov_iter and iomem

Add two more helpers for copying memory between iov_iter and iomem,
which will be used by the new PCM copy ops in a few drivers.
The existing helpers became wrappers of those now.

Note that copy_from/to_iter() returns the copied bytes, hence the
error condition is adjusted accordingly.

Link: https://lore.kernel.org/r/20230815190136.8987-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>