video: tegra: host: gk20a: Export raw counters

video: tegra: host: gk20a: Export raw counters

GPU scaling in user space is moving towards using raw counter
readings instead of instantaneous load. This patch exports busy
and idle counters to userspace as sysfs nodes counters and
counters_reset. The first node shows raw counter values and
the second node shows the raw values and resets them.

This patch does not account for possible wrapping issues.

Bug 1444343

Change-Id: I24620a77f5042008ac811ed55cb1b0d1ea3eac37
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-on: http://git-master/r/359240
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>