gpu: nvgpu: modify the ffs and fls interface

Modify the ffs/fls interface function names to nvgpu_ffs and
nvgpu_fls.  The return bit values are numbered from 1 to 64.
A return value of 0 indicates an input of 0 value.

Jira NVGPU-3601

Change-Id: I1c151eeac1f94fe3b5b85bd5daf0488f75c5efa0
Signed-off-by: ajesh <akv@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2146119
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svc-mobile-misra <svc-mobile-misra@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Philip Elcan <pelcan@nvidia.com>
Reviewed-by: Nitin Kumbhar <nkumbhar@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

userspace/units/fifo/nvgpu-fifo.c

@@ -47,7 +47,7 @@ bool test_fifo_subtest_pruned(u32 branches, u32 final_branches)
 	if (match == 0U) {
 		return false;
 	}
-	bit = ffs(match) - 1;
+	bit = nvgpu_ffs(match) - 1;
 
 	return (branches > BIT(bit));
 }