serial: dcc: Move driver to DM

Enabling this driver requires some DT changes.
Adding DCC to root or main bus:
dcc: dcc {
	compatible = "arm,dcc";
	u-boot,dm-pre-reloc;
};

Extend alias list to link DCC:
	serial0 = &uart0;
	serial1 = &uart1;
	serial2 = &dcc;

Change stdout-path to point to dcc port.
	stdout-path = "serial2:115200n8";

Also add support for debug uart to help with early debug.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>