hv: remove the usage of 'atoi()'

this function is not from libc but has the same name,
  atoi() in libc is unbounded and not safe.

  replace this function with 'strtol_deci()' in this case.

Tracked-On: #2187
Signed-off-by: Yonghua Huang <yonghua.huang@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/lib/string.c

@@ -157,11 +157,6 @@ uint64_t strtoul_hex(const char *nptr)
 	return acc;
 }
 
-int32_t atoi(const char *str)
-{
-	return (int32_t)strtol_deci(str);
-}
-
 char *strchr(char *s_arg, char ch)
 {
 	char *s = s_arg;