gpu: nvgpu: unit test for common-io

This patch covers unit test for nvgpu_writel_check().

Jira NVGPU-4810

Change-Id: I173afd59a9e8fe9e647f260a70012f2c7c2d02f9
Signed-off-by: Prateek sethi <prsethi@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2293538
Reviewed-by: Rajesh Devaraj <rdevaraj@nvidia.com>
Reviewed-by: Ankur Kishore <ankkishore@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit

userspace/SWUTS.h

@@ -152,5 +152,7 @@
  *   - @ref SWUTS-ecc
  *   - @ref SWUTS-channel_devctl_qnx
  *   - @ref SWUTS-pmu
+ *   - @ref SWUTS-io
+ *
  */