string: implement strspn, strcspn, atol

Change-Id: Id8fa880357124b620bde8884949bd8ffff7d0762
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34450
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/include/string.h

@@ -32,6 +32,9 @@ char *strncpy(char *to, const char *from, int count);
 char *strcpy(char *dst, const char *src);
 int strcmp(const char *s1, const char *s2);
 int strncmp(const char *s1, const char *s2, int maxlen);
+int strspn(const char *str, const char *spn);
+int strcspn(const char *str, const char *spn);
+long atol(const char *str);
 
 /**
  * Find a character in a string.