gpio: generic: make bgpio_pdata always visible

Board files that define their own bgpio_pdata are broken when
CONFIG_GPIO_GENERIC is disabled and the bgpio_pdata structure
definition is hidden by the #ifdef:

arch/arm/mach-clps711x/board-autcpu12.c:148:15: error: variable 'autcpu12_mmgpio_pdata' has initializer but incomplete type
 static struct bgpio_pdata autcpu12_mmgpio_pdata __initdata = {
arch/arm/mach-clps711x/board-autcpu12.c:149:2: error: unknown field 'base' specified in initializer
  .base = AUTCPU12_MMGPIO_BASE,

Since the board files should generally not care what drivers are
enabled, this makes the structure definition visible again.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 0f4630f3 ("gpio: generic: factor into gpio_chip struct")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>