gpu: nvgpu: Enabling/disabling FECS trace support

- To enable FECS trace support, nvgpu should set the MSB
of the read pointer (MAILBOX1).
- The ucode will check if the feature is enabled/disabled
before writing a record into the circular buffer. If the
feature is disabled, it will not write the record.
- If the feature is enabled and the buffer is not allocated,
HW will throw a page fault error.

Bug 2459186

Change-Id: I71daf6fdb1bb67974f6e51e091f868cb08d3b0bf
Signed-off-by: Vaibhav Kachore <vkachore@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2111028
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/include/nvgpu/enabled.h

@@ -37,6 +37,7 @@ struct gk20a;
 #define NVGPU_FECS_TRACE_VA			4
 #define NVGPU_CAN_RAILGATE			5
 #define NVGPU_KERNEL_IS_DYING			6
+#define NVGPU_FECS_TRACE_FEATURE_CONTROL	7
 
 /*
  * ECC flags