gpio/mxc: move irq_domain_add_legacy call into gpio driver

Move irq_domain_add_legacy call from imx*-dt.c into gpio driver and
have the gpio driver adopt irqdomain support for both DT and non-DT
boot.

With all imx platform code converted from static gpio irq number
computation to use run-time gpio_to_irq call, we can now use
irq_alloc_descs and irqdomain support to dynamically get irq_base
and have the mapping between gpio and irq number available without
using virtual_irq_start and MXC_GPIO_IRQ_START.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Dong Aisheng <dong.aisheng@linaro.org>

arch/arm/mach-imx/imx27-dt.c

@@ -40,21 +40,8 @@ static int __init imx27_avic_add_irq_domain(struct device_node *np,
 	return 0;
 }
 
-static int __init imx27_gpio_add_irq_domain(struct device_node *np,
-				struct device_node *interrupt_parent)
-{
-	static int gpio_irq_base = MXC_GPIO_IRQ_START + ARCH_NR_GPIOS;
-
-	gpio_irq_base -= 32;
-	irq_domain_add_legacy(np, 32, gpio_irq_base, 0, &irq_domain_simple_ops,
-				NULL);
-
-	return 0;
-}
-
 static const struct of_device_id imx27_irq_match[] __initconst = {
 	{ .compatible = "fsl,imx27-avic", .data = imx27_avic_add_irq_domain, },
-	{ .compatible = "fsl,imx27-gpio", .data = imx27_gpio_add_irq_domain, },
 	{ /* sentinel */ }
 };