PCI/pwrctrl: slot: Factor out power on/off code to helpers

PCI/pwrctrl: slot: Factor out power on/off code to helpers

In order to allow the pwrctrl core to control the power on/off logic of the
pwrctrl slot driver, move the power on/off code to
pci_pwrctrl_slot_power_{off/on} helper functions.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260115-pci-pwrctrl-rework-v5-7-9d26da3ce903@oss.qualcomm.com