gpio: ep93xx: fix BUG_ON port F usage

Two index spaces and ep93xx_gpio_port are confusing.

Instead add a separate struct to store necessary data and remove
ep93xx_gpio_port.

- add struct to store IRQ related data for each IRQ capable chip
- replace offset array with defined offsets
- add IRQ registers offset for each IRQ capable chip into
  ep93xx_gpio_banks

------------[ cut here ]------------
kernel BUG at drivers/gpio/gpio-ep93xx.c:64!
---[ end trace 3f6544e133e9f5ae ]---

Fixes: fd935fc4 ("gpio: ep93xx: Do not pingpong irq numbers")
Cc: <stable@vger.kernel.org>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>