ALSA: Add helper function for intersecting two rate masks

ALSA: Add helper function for intersecting two rate masks

A bit of special care is necessary when creating the intersection of two rate
masks. This comes from the special meaning of the SNDRV_PCM_RATE_CONTINUOUS and
SNDRV_PCM_RATE_KNOT bits, which needs special handling when intersecting two
rate masks. SNDRV_PCM_RATE_CONTINUOUS means the hardware supports all rates in a
specific interval. SNDRV_PCM_RATE_KNOT means the hardware supports a set of
discrete rates specified by a list constraint. For all other cases the supported
rates are specified directly in the rate mask.

Signed-off-by: Lars-Peter Clausen <[email protected]>
Reviewed-by: Takashi Iwai <[email protected]>
Signed-off-by: Mark Brown <[email protected]>