dm: ns16550: Add support for reg-offset property

reg-offset is the part of standard 8250 binding in the kernel.
It is shifting start of address space by reg-offset.
On Xilinx platform this offset is typically 0x1000.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Moved the new field to the end of the struct to avoid problems:
Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/serial/ns16550.c

@@ -105,7 +105,7 @@ static void ns16550_writeb(NS16550_t port, int offset, int value)
 	 * As far as we know it doesn't make sense to support selection of
 	 * these options at run-time, so use the existing CONFIG options.
 	 */
-	serial_out_shift(addr, plat->reg_shift, value);
+	serial_out_shift(addr + plat->reg_offset, plat->reg_shift, value);
 }
 
 static int ns16550_readb(NS16550_t port, int offset)
@@ -116,7 +116,7 @@ static int ns16550_readb(NS16550_t port, int offset)
 	offset *= 1 << plat->reg_shift;
 	addr = map_physmem(plat->base, 0, MAP_NOCACHE) + offset;
 
-	return serial_in_shift(addr, plat->reg_shift);
+	return serial_in_shift(addr + plat->reg_offset, plat->reg_shift);
 }
 
 /* We can clean these up once everything is moved to driver model */
@@ -401,6 +401,8 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
 		return -EINVAL;
 
 	plat->base = addr;
+	plat->reg_offset = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
+				     "reg-offset", 0);
 	plat->reg_shift = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
 					 "reg-shift", 0);
 	plat->clock = fdtdec_get_int(gd->fdt_blob, dev->of_offset,

include/ns16550.h

@@ -56,6 +56,7 @@ struct ns16550_platdata {
 	unsigned long base;
 	int reg_shift;
 	int clock;
+	int reg_offset;
 };
 
 struct udevice;