gpio: bt8xx: use generic power management

gpio: bt8xx: use generic power management

Switch to the generic PCI power management framework and remove legacy
callbacks like .suspend() and .resume(). With the generic framework, the
standard PCI related work like:
	- pci_save/restore_state()
	- pci_enable/disable_device()
	- pci_set_power_state()
is handled by the PCI core and this driver should implement only gpio-bt8xx
specific operations in its respective callback functions.

Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20251016163618.1355923-1-vaibhavgupta40@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>