Support source device to MSD sink device direct patching

Currently, device to device software patches between different
hardware modules route to a sink's PCM opened output stream. To
support compressed / direct audio patching from HDMI inputs to MSD,
build an explicit MSD patch between the source device and MSD, which
has the advantage of supporting preferential audio configuration
selection (e.g. IEC60958 over PCM).

This change also updates existing MSD methods to reflect that they
operate on MSD output (MSD source to downstream) patches only.

This change also adds IEC60958 as the most preferred MSD patch format
as it is suitable for transmission of both PCM and compressed audio.

Bug: 181102125
Test: atest audiopolicy_tests
Change-Id: I259a15ac88e45f6bef5180a44967a58facfcfb56