gpio: omap: Fix lost edge interrupts

Now acking of edge irqs happens the following way:
- omap_gpio_irq_handler
  - "isr" = read irq status
  - omap_clear_gpio_irqbank(bank, isr_saved & ~level_mask);
	^ clear edge status, so irq can be accepted
  - loop while "isr"
	generic_handle_irq()
	 - handle_edge_irq()
	    - desc->irq_data.chip->irq_ack(&desc->irq_data);
		- omap_gpio_ack_irq()
it might be that at this moment edge IRQ was triggered again and it will be
cleared and IRQ will be lost.

Use handle_simple_irq and clear edge interrupts early without disabling them in
omap_gpio_irq_handler to avoid loosing interrupts.

[1] https://marc.info/?l=linux-omap&m=149004465313534&w=2


Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>