Enable DT based earlycon initialization for the pl011 uart.
Signed-off-by: Rob Herring <robh@kernel.org> Cc: Russell King <linux@arm.linux.org.uk> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.cz> Acked-by: Grant Likely <grant.likely@linaro.org>