liblog: clock_gettime, clock_getres and time benchmarks

Add local BM_time_clock_gettime_*, BM_time_clock_getres_* and
BM_time_time benchmarks.  Relates to the bionic benchmarks of
the same names, except adds CLOCK_MONOTONIC_RAW.  Added here for
developer convenience whenever updates to the liblog or logd
code base need integration testing.

ToDo: add liblog gTests that analyse the benchmark data to confirm
that the specified integrated device has vdso access to all the
pertinent clock sources.  Add liblog local benchmarks and tests to
measure the device clock drift of each possible liblog clock
source to help evaluate device configuration.

Test: liblog_benchmarks --benchmark_filter=BM_time*
Bug: 63737556
Bug: 69423514
Change-Id: Ibafe0880d976ef2b3885765f71e0ba6c99d56f2a