CSD: Add logic for forcing the use of internal MEL

This flag should be used for testing purposes only. Sometimes it might
make sense to disable the HAL sound dose interface to test the internal
MEL computation and sound dose logic end-2-end.

Test: sounddosemanager_tests UT
Bug: 248565894
Change-Id: Ieaf506511c0aee3b9a5a262831b950d9dcaf3535