Allow media.codec and media.extractor to specify two policy files.

Bug: Bug: 34723744
Test: Unit tests.
Test: media.codec, media.extractor start, have Seccomp.
Test: cat /proc/`pgrep .codec`/status | grep Seccomp
      Seccomp:    2
Test: cat /proc/`pgrep .extractor`/status | grep Seccomp
      Seccomp:    2
Change-Id: If5c3dcc934f5d76bd32859b2f7b7ecb772a56303