MIPS: EMMA2RH: Use handle_edge_irq() handler for GPIO interrupts

EMMA's GPIO interrupts are latched by GPIO interrupt status register.
In this case, we're encouraged to use handle_edge_irq() handler.

The following changes are made along with replacing set_irq_chip() with
set_irq_chip_and_handler_name(,,handle_edge_irq,"edge"):

* Fix emma2rh_gpio_irq_ack not to disable interrupts

  With handle_edge_irq(), we're not expected to disable interrupts
  when chip->ack is served, so fix it accordingly.  We also add a new
  emma2rh_gpio_irq_mask_ack() for chip->mask_ack operation, instead.

* Remove emma2rh_gpio_irq_end(), as chip->end is no longer served.

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi@necel.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>