Refactor HwCrypto sample code

Refactored HwCrypto sample code to use handle
sets instead of the old style communication
channel message handling. This also fixes an
issue with the old rng code if more data than
the available communication buffer is requested,
causing the service to hang.

Bug: 336802160
Test: build & run com.android.trusty.hwcrypto.test/
      com.android.trusty.hwrng.test
Change-Id: I5d305312d52037c9dab20be46c5c95774f853a73