ep93xx: fix build of vision_ep93xx.c

Fix build breakage due to the following commits:

Commit bd5f12a2
  ARM: 7042/3: mach-ep93xx: break out GPIO driver specifics

Commit 257af9f9
  ARM: 7041/1: gpio-ep93xx: hookup the to_irq callback in the driver

The vision_ep9307 machine uses the ep93xx build-in gpios and needs to
include <mach/gpio-ep93xx.h> to pickup the defines.

The gpio_to_irq() call is now a callback to the gpio-ep93xx.c driver
and cannot be used as a constant initializer for the .irq member of
struct i2c_board_info.

Signed-off-by: Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Ryan Mallon <rmallon@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>