mcp23s08: add i2c support

mcp23s08: add i2c support

Add i2c bindings for the mcp230xx devices. This is quite a lot simpler
than the spi one as there's no funky sub addressing done (one struct
i2c_client per struct gpio_chip).

The mcp23s08_platform_data structure is reused for i2c, even though
only a single mcp23s08_chip_info structure is needed.

To use, simply fill out a platform_data structure and pass it in
i2c_board_info, E.G.:

static const struct mcp23s08_platform_data mcp23017_data = {
	.chip[0] = {
		.pullups = 0x00ff,
	},
	.base = 240,
};

static struct i2c_board_info __initdata i2c_devs[] = {
	{ I2C_BOARD_INFO("mcp23017", 0x20),
	  .platform_data = &smartview_mcp23017_data, },
	...
};

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>