powerpc/52xx: Replace of_gpio.h by proper one

of_gpio.h is deprecated and subject to remove.
The driver doesn't use it directly, replace it
with what is really being used.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240313135645.2066362-1-andriy.shevchenko@linux.intel.com