IOMX: add API for setPortMode

- Add setPortMode to centralize port mode configuration

- Remove storeMetaDataInBuffers and enableNativeBuffers. These are
  no longer exposed to the client. Metadata mode and native/secure
  buffer mode will be enabled by OMX as needed by the port mode.

- Move handling of legacy adpative experiment (legacy metadata mode)
  to OMX side. Legacy mode will now appear the same as non-metadata
  mode to client.

bug: 31399200

Change-Id: Iaf33bd7c30fab4acbc19e9fb8c19e322f9b4a0a0