PCI: imx6: Move imx6_pcie_reset_phy() near other PHY handling functions

Move imx6_pcie_reset_phy() near the other PHY related functions in the
file.  This is a cosmetic change, but also allows to do the following
changes without introducing needless forward declarations.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>