Prepare for having audio_channel_mask_t as an enum type

audio_channel_mask_t used to be an alias for uint32_t, but
it will become an enum type. To facilitate this conversion,
bit operations involving audio_channel_mask_t must coerce type.

Bug: 169889714
Test: m
Merged-In: I42506484b1d0b0482618b7314fad4c8012a06fb4
Change-Id: I48f472b687159533092d6ae366f05a0a68c2554a