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/Kconfig.debug

@@ -37,4 +37,14 @@ config DEBUG_STACK_USAGE
 	  stack seen so far.
 
 	  This option will slow down process creation and destruction somewhat.
+
+config EARLY_PRINTK
+	bool "Early printk"
+	default y
+	---help---
+	  Write kernel log output directly to stdout.
+
+	  This is useful for kernel debugging when your machine crashes very
+	  early before the console code is initialized.
+
 endmenu