MFC r308428:

Refactor FDT part of gpioled driver

- Split driver in two parts: FDT and non-FDT
- Instead of reattach gpioled nodes to GPIO bus use
gpio_pin_get_by_ofw_idx and add ofwbus and simplebus as parrent buses

Reviewed by: loos
Differential Revision: https://reviews.freebsd.org/D8233