Add additional optional audio/x-mpeg MIME type to MIME type map

audio/x-mpeg is a valid MIME type and still being used by some apps.

Bug: 157127219
Test: atest CtsMimeMapTestCases
Change-Id: I43d18d419a282ff0ca3ca5f2773d7002fcb62014

mime/java-res/android.mime.types

@@ -84,6 +84,7 @@
 ?audio/sp-midi smf
 ?audio/x-matroska mka
 ?audio/x-pn-realaudio ra
+?audio/x-mpeg mp3
 
 ?image/bmp bmp
 ?image/heic heic