gpu: nvgpu: APIs to dump GR status

gpu: nvgpu: APIs to dump GR status

Add below APIs to dump various GR status registers

1. debugfs : /d/gpu.0/gr_status
Read this debugfs at runtime to get status registers

2. API gk20a_gr_debug_dump()
Add this API in code to dump registers at any point

Bug 200062436

Change-Id: Ic1115b5a2fc16362954b5ed8a9e70afb872a8d91
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/486465
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>