BSP benchmark timer to be replaced with RTEMS counter support?

[Amaan Cheval]

The BSP porting guide[1] includes this warning when talking about the
benchmark timer driver:

> The Timer Driver is superfluous and should be replaced by the RTEMS
counter support. Ask on the mailing list if you plan to write a Timer
Driver.

We also have this[2] open ticket about the same issue. It seems like this
might be a part of the BSP's clock driver, exposed through the
"_CPU_Counter_read" function. Is that right?

The tests in ./testsuites/tmtests/ do call several benchmark_timer_*
functions, so I imagine the warning means that we can implement these
functions using the counter instead of reading the hardware timer by itself
as the guide shows?

(For context: this is relevant to my GSoC plan for the x86_64 port and BSP;
I'd like to architect it to be of a style which the RTEMS community deems
ideal, despite other BSPs not quite being there yet, understandably.)

[1] https://docs.rtems.org/branches/master/bsp-howto/timer.html
[2] https://devel.rtems.org/ticket/2847