PCI: dwc: imx6: Share PHY debug register definitions

Both pcie-designware.c and pci-imx6.c contain custom definitions for
PHY debug registers R0/R1 and on top of that there's already a
definition for R0 in pcie-designware.h. Move all of the definitions to
pcie-designware.h. No functional change intended.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: linux-pci@vger.kernel.org