gpio: mcp23s08 to support both device tree and platform data

Device tree is not enabled in some architecture where gpio
driver mcp23s08 is still required.

v2-changes:
- Parse device tree properties into platform data other than
  individual variables.
v3-changes:
- Use of_node in gpio_chip device structure, because the
  struct device * always has an of_node which is NULL when
  OF is not used.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/spi/mcp23s08.h

@@ -22,4 +22,22 @@ struct mcp23s08_platform_data {
 	 * base to base+15 (or base+31 for s17 variant).
 	 */
 	unsigned	base;
+	/* Marks the device as a interrupt controller.
+	 * NOTE: The interrupt functionality is only supported for i2c
+	 * versions of the chips. The spi chips can also do the interrupts,
+	 * but this is not supported by the linux driver yet.
+	 */
+	bool		irq_controller;
+
+	/* Sets the mirror flag in the IOCON register. Devices
+	 * with two interrupt outputs (these are the devices ending with 17 and
+	 * those that have 16 IOs) have two IO banks: IO 0-7 form bank 1 and
+	 * IO 8-15 are bank 2. These chips have two different interrupt outputs:
+	 * One for bank 1 and another for bank 2. If irq-mirror is set, both
+	 * interrupts are generated regardless of the bank that an input change
+	 * occurred on. If it is not set, the interrupt are only generated for
+	 * the bank they belong to.
+	 * On devices with only one interrupt output this property is useless.
+	 */
+	bool		mirror;
 };