intel_gpu_top: support non-interactive mode

intel_gpu_top: support non-interactive mode

This patch adds support for non-interactive mode, invoked by running with
'-o output' switch. In this case, no interactive output is being
performed, but the execution statistics are being saved into the output
file.

The output file is generated in both human and gnuplot-readable format.

Unlike interactive mode, where non-supported pipes and non-active
registers are skipped, the content of such pipes and registers is recorded
into the log file to simplify parsing and standardize the list of columns.

Also, unlike interactive mode, the registers are not sorted according to
the usage - this way, their variation over time can be analysed offline.

Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>