[POWERPC] Fix console output getting dropped on platforms without udbg_putc

Previously, registering this early console would just result
in dropping early buffered printk output until a udbg_putc
was registered.

However, commit 69331af79c
clears the CON_PRINTBUFFER flag on the main console when a
CON_BOOT (early) console has been registered, resulting in
the buffered messages never being displayed to the user.

This fixes the problem by making sure we don't register udbg_console
on platforms that don't implement udbg_putc.

Signed-off-by: Milton Miller <miltonm@bga.com>
Acked-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/udbg.c

@@ -151,12 +151,18 @@ static struct console udbg_console = {
 
 static int early_console_initialized;
 
-/* called by setup_system */
+/*
+ * Called by setup_system after ppc_md->probe and ppc_md->early_init.
+ * Call it again after setting udbg_putc in ppc_md->setup_arch.
+ */
 void register_early_udbg_console(void)
 {
 	if (early_console_initialized)
 		return;
 
+	if (!udbg_putc)
+		return;
+
 	if (strstr(boot_command_line, "udbg-immortal")) {
 		printk(KERN_INFO "early console immortal !\n");
 		udbg_console.flags &= ~CON_BOOT;