S5P: Serial: Add fdt support to driver

S5P: Serial: Add fdt support to driver

This patch adds FDT support to the serial s5p driver.
At present disabling the serial console (from the device tree) crashes
U-Boot. Add checks for this case, so that execution can continue without
a serial console.
It also enables the serial_s5p driver recognize the silent_console option.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Gabe Black <gabeblack@google.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rajeshwari Shinde <rajeshwari.s@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>