Cameraservice: Cache camera service proxy interface

To improve camera launch performance, cache the proxy service
interface.  System tracing indicates fetching the interface can take
up to 8-10 ms during real camera opens, which is a percent or two
of total camera startup time.

Test: atest CameraCtsTestCases
Bug: 130173970
Change-Id: Icdf5218b04f608b897dcbf2085f971b04a913f3b