Fix clang-tidy warnings in drm.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
* Use const reference type to avoid unnecessary copy.
Bug: 30413862
Test: build with WITH_TIDY=1

Change-Id: Idf1c48d7bfe3f0da20401cb3ff1983ec00be170d
18 files changed