Update HIDL-related documentation.

This is a followup CL to previous @SystemApi CLs.

Bug: N/A
Test: N/A
Change-Id: I9c7dcc776dcfb89fd90afa4fc5d74e40ff0a5f94
Merged-In: I9c7dcc776dcfb89fd90afa4fc5d74e40ff0a5f94
(cherry picked from commit 739811a5c53e435b3f0cfd5abf58389416be429c)
3 files changed