Permits using KGDB over the console with the atmel_serial driver.

[akpm@linux-foundation.org: s/barrier/cpu_relax/]
Signed-off-by: NAlbin Tonnerre <albin.tonnerre@free-electrons.com>
Acked-by: NAndrew Victor <linux@maxim.org.za>
Acked-by: NHaavard Skinnemoen <haavard.skinnemoen@atmel.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>