Support dynamic 64-bit media service

64-bit GSI requires support both 64_32-bit and 64-bit devices at
the same time. Add a new variable TARGET_DYNAMIC_64_32_MEDIASERVER
to put mediaserver_dynamic.rc into GSI. Which starts 64-bit
mediaserver if ro.zygote is zygote64. Otherwise, it keeps the
original behavior to start 32-bit meidaserver.

Bug: 236664614
Test: make gsi_arm64-user; Check system/etc/init
Test: make gsi_arm-user; Check systen/etc/init
Test: cts-tradefed; run cts-on-gsi -m CtsViewTestCases
Change-Id: I74699ec5fafadcbe78a7fef6d10aaed752cd5afa