treewide: Move skip_atoi function to commonlib

BUG=none
TEST=Build and verify on Screebo
TEST=make unit-tests

```
$ make tests/commonlib/bsd/string-test
[==========] tests_commonlib_bsd_string-test(tests): Running 1 test(s).
[ RUN      ] test_skip_atoi
[       OK ] test_skip_atoi
[==========] tests_commonlib_bsd_string-test(tests): 1 test(s) run.
[  PASSED  ] 1 test(s).
```

Change-Id: Ifaaa80d0c696a625592ce301f9e3eefb2b4dcd98
Signed-off-by: Maximilian Brune <maximilian.brune@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82910
Reviewed-by: Jakub Czapiga <czapiga@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/commonlib/bsd/string.c

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+
+#include <commonlib/bsd/string.h>
+#include <ctype.h>
+
+unsigned int skip_atoi(char **ptr)
+{
+	unsigned int result = 0;
+	char *str;
+
+	for (str = *ptr; isdigit(str[0]); str++)
+		result = result * 10 + (str[0] - '0');
+	*ptr = str;
+	return result;
+}