HAL: Add facade for fetching incoming HCI packets

Adding the event stream primitives. General event stream request is
defined in facade/common.proto. "grpc/grpc_event_stream.h" provides
helper class templates GrpcEventStreamCallback and GrpcEventStream to
help user handle EventStream request without writing boilerplate code.

Test: cert/run_cert.sh
Change-Id: I00b51fc7b1faefb7c97cc647876f41854872a415