media: stagefright: Implement TARGET_USE_SOFTWARE_AUDIO_AAC in OMXCodec

In its current state, harmony devices will encounter a dump, if HW AAC
is attempted to be used.

When TARGET_USE_SOFTWARE_AUDIO_AAC : true is set in BoardConfig.mk, software
will be used.

Change-Id: I4be89407f15898742301f8cd1b451cfa5a599621