gpio: dwapb: Append MODULE_ALIAS for platform driver

The commit 3d2613c4
  ("GPIO: gpio-dwapb: Enable platform driver binding to MFD driver")
introduced a use of the platform driver but missed to add the following line
to it:
  MODULE_ALIAS("platform:gpio-dwapb");

Add this to get driver loaded automatically if platform device is registered.

Fixes: 3d2613c4 ("GPIO: gpio-dwapb: Enable platform driver binding to MFD driver")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20200415141534.31240-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>