gpio: dwapb: Add support for 1 interrupt per port A GPIO

The DesignWare GPIO IP can be configured for either 1 interrupt or 1
per GPIO in port A, but the driver currently only supports 1 interrupt.
See the DesignWare DW_apb_gpio Databook description of the
'GPIO_INTR_IO' parameter.

This change allows the driver to work with up to 32 interrupts, it will
get as many interrupts as specified in the DT 'interrupts' property.
It doesn't do anything clever with the different interrupts, it just calls
the same handler used for single interrupt hardware.

ACPI companion code provided by Hoan Tran <hotran@apm.com>. This was tested
on X-Gene by Hoan.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Hoan Tran <hotran@apm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>