serial: 8250_early: Add earlycon support for Synopsys DesignWare ABP UART

Some board like Hisilicon D02 uses Synopsys DesignWare ABP UART, declare an
OF early console for it, so early console device can be enabled with comand
line "earlycon"(without option) via the "stdout-path" property in device-tree.
Signed-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: NJon Mason <jon.mason@broadcom.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_early.c

@@ -150,6 +150,7 @@ EARLYCON_DECLARE(uart, early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
 OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
+OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
 
 #ifdef CONFIG_SERIAL_8250_OMAP