gpu: nvgpu: unit: add coverage tests for gops.gr.init.ecc_scrub_reg

Add new unit test to cover gops.gr.init.ecc_scrub_reg HAL function

gops.gr.init.ecc_scrub_reg HAL can generate TIMEOUT errors which are
not returned to caller currently. Update this HAL to return int value
for error propagation.

Jira NVGPU-4458

Change-Id: I98f4d5af2ef17cc4301951fec4d660638c8ef72c
Signed-off-by: dnibade <dnibade@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2265456
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

userspace/required_tests.json

@@ -2501,6 +2501,12 @@
         "unit": "nvgpu_gr_init",
         "test_level": 0
     },
+    {
+        "test": "test_gr_init_hal_ecc_scrub_reg",
+        "case": "gr_init_hal_ecc_scrub_reg",
+        "unit": "nvgpu_gr_init",
+        "test_level": 0
+    },
     {
         "test": "test_gr_remove_setup",
         "case": "gr_remove_setup",