gpio: xgene-sb: Drop redundant OF_GPIO dependency

gpio: xgene-sb: Drop redundant OF_GPIO dependency

There is nothing in the driver requires OF_GPIO. Moreover, driver
supports ACPI and OF_GPIO may be a quite overhead on such configurations.

Drop dependency for good and replace of_gpio.h to of.h since we have
one function to be defined from there.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200512182721.55127-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>