gpu: nvgpu: fix MISRA 21.6 violation in nvgpu.common.mm.as

Below MISRA 21.6 violation is reported in nvgpu.common.mm.as

${TEGRA_TOP}/kernel/nvgpu/drivers/gpu/nvgpu/common/mm/as.c:79:
misra_violation: Using function "snprintf".

Fix this by replacing snprintf with strncpy.
Add nvgpu_strnadd_u32 function to convert u32 to string
The function supports radix from 2 to 16.

Jira NVGPU-3333

Change-Id: Idee739dfdedeabb74d0d9f7d4cddd798445f0ee1
Signed-off-by: Thomas Fleury <tfleury@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2117019
GVS: Gerrit_Virtual_Submit
Reviewed-by: Philip Elcan <pelcan@nvidia.com>
Reviewed-by: Vaibhav Kachore <vkachore@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/common/string.c

@@ -21,6 +21,7 @@
  */
 
 #include <nvgpu/string.h>
+#include <nvgpu/log.h>
 
 void
 nvgpu_memcpy(u8 *destb, const u8 *srcb, size_t n)
@@ -33,3 +34,46 @@ nvgpu_memcmp(const u8 *b1, const u8 *b2, size_t n)
 {
 	return memcmp(b1, b2, n);
 }
+
+int nvgpu_strnadd_u32(char *dst, const u32 value, size_t size, u32 radix)
+{
+	int n;
+	u32 v;
+	char *p;
+	u32 digit;
+
+	if (radix < 2U || radix > 16U) {
+		return 0;
+	}
+
+	/* how many digits do we need ? */
+	n = 0;
+	v = value;
+	do {
+		n++;
+		v = v / radix;
+	} while (v > 0U);
+
+	/* bail out if there is not room for '\0' */
+	if (n >= (int)size) {
+		return 0;
+	}
+
+	/* number of digits (not including '\0') */
+	p = dst + n;
+
+	/* terminate with '\0' */
+	*p = '\0';
+	p--;
+
+	v = value;
+	do {
+		digit = v % radix;
+		*p = "0123456789abdcef"[digit];
+		v = v / radix;
+		p--;
+	}
+	while (v > 0U);
+
+	return n;
+}