cobalt_read_hrclock() returns the current TSC value as defined by the
platform. This is a Cobalt-specific service, which is aimed at
measuring elapsed time accurately, with low overhead. The output is
the current raw count of ticks, as reported by the hrclock device used
by Cobalt for timing.

Such value is NOT converted to nanoseconds before return.
cobalt_ticks_to_ns() and cobalt_ticks_to_ns_rounded() are available
for converting raw tick counts to nanoseconds.

Application code should stick with clock_gettime(CLOCK_MONOTONIC, ...)
for portability.

This clock source is guaranteed continuous, monotonically increasing.