builtin: support uid/gid config for binfs app

Implement I_SUID/I_SGID feature for binfs in the POSIX compliant way.
If set-user-ID bit is set in the file permissions, then the effective
user ID of process shall be set to UID of the new process image file.

test case:
hello example emulates to set uid and file set-user-ID bit, and call
geteuid and getegid API.
UID  = 2000
GID  = 3000
MODE = 06555

nsh> ls -l /bin/hello
 -r-sr-sr-x    2000    3000       0 hello
nsh> hello
geteuid:2000
getegid:3000

Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>

binfmt/builtin.c

@@ -106,6 +106,12 @@ static int builtin_loadbinary(FAR struct binary_s *binp,
   binp->entrypt   = builtin->main;
   binp->stacksize = builtin->stacksize;
   binp->priority  = builtin->priority;
+#ifdef CONFIG_SCHED_USER_IDENTITY
+  binp->uid       = builtin->uid;
+  binp->gid       = builtin->gid;
+  binp->mode      = builtin->mode;
+#endif
+
   return OK;
 }