ARM: Add an earlyprintk debug console

This patch allows an earlyprintk console if CONFIG_DEBUG_LL is enabled,
using the printch asm function.

The patch is based on the original work by Sascha Hauer.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Pavel Machek <pavel@ucw.cz>

arch/arm/Kconfig.debug

@@ -71,6 +71,14 @@ config DEBUG_LL
 	  in the kernel.  This is helpful if you are debugging code that
 	  executes before the console is initialized.
 
+config EARLY_PRINTK
+	bool "Early printk"
+	depends on DEBUG_LL
+	help
+	  Say Y here if you want to have an early console using the
+	  kernel low-level debugging functions. Add earlyprintk to your
+	  kernel parameters to enable this console.
+
 config DEBUG_ICEDCC
 	bool "Kernel low-level debugging via EmbeddedICE DCC channel"
 	depends on DEBUG_LL