sepolicy: Add support for fastbootd to flash dynamic partitions

Sepolicy changes needed for dynamic partition support for legacy
targets : SDM845 and SDM710
- Add rules to enable fastbootd mode flashing of dynamic partition
- Define labels for super, recovery and vbmeta_system partitions
- Allow update_engine to access recovery partition for OTA

Change-Id: I6f692da6ab687529833a87b6feb375fda26508b8