mediacodec: add seccomp policy for x86 and x86_64

We had it for arm but not for x86; this cl adds it.

BUG: 70507558

Test: run cts -m CtsMediaTestCases and mediacodec should not
crash due to minijail
Test: launch emulator and mediacodec should not be killed by signal 31
Test: run cts -m CtsSecurityHostTestCases
-t android.security.cts.ProcessMustUseSeccompTest#testOmxHalHasSeccompFilter
should pass
Test: run cts -m CtsSecurityTestCases -t
android.security.cts.StagefrightTest#testStagefright_cve_2017_0600
Test: run cts -m CtsSecurityTestCases -t
android.security.cts.StagefrightTest#testStagefright_cve_2016_0842

Note: I only tested on emulator, not on real x86 device

Change-Id: I63bebc17eb2ae29df71823f8277f058ca7fd9625
Merged-In: I63bebc17eb2ae29df71823f8277f058ca7fd9625