audio: Allow using vendor extensions in surround formats (V6)

The 'surroundFormats' section must allow specifying
vendor-provided formats (vendor extensions). This has been
fixed in Audio HAL V7. Backporting to earlier versions.

Bug: 173647783
Test: atest VtsHalAudioV6_0TargetTest
Change-Id: I8ae1687087bab3f1c9020f351bdf7b81b9e74e50