um: add earlyprintk support

User Mode Linux can also benefit from earlyprintk.  UML's earlyprintk
writes kernel messages directly to stdout.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/os-Linux/util.c

@@ -139,3 +139,8 @@ void os_dump_core(void)
 
 	uml_abort();
 }
+
+void um_early_printk(const char *s, unsigned int n)
+{
+	printf("%.*s", n, s);
+}