legacy OMX: use local flags

Allows use of legacy mmparser without enabling all QCOM A/V
enhancements that are not supported with legacy OMX blobs.

Enable by setting TARGET_QCOM_LEGACY_OMX := true in BoardConfig.mk.

Change-Id: Ieccf29ed8036864634ee167c1e21908377516494

Conflicts:
	media/libstagefright/Android.mk