Revert "ath79: remove GPIO driver earlier registration hack"

Revert "ath79: remove GPIO driver earlier registration hack"

This reverts commit f444dea428cdcafd78fb75004a942da24cabd48c.

It seems that some devices using GPIO WDT have really short WDT timeouts
and when using module_platform_driver registration it happens too late
and thus WDT will timeout and reset the board.

So, for now lets return the postcore_initcall hack for now.

Fixes: f444dea428cd ("ath79: remove GPIO driver earlier registration hack")
Signed-off-by: Joan Moreau <jom@grosjo.net>
Link: https://github.com/openwrt/openwrt/pull/16035
Signed-off-by: Robert Marko <robimarko@gmail.com>