PCI: dwc: artpec6: Deassert the core before waiting for PHY

Waiting for the PHY while the core was held in reset worked for artpec6,
but for artpec7, in order to read the required registers, the core has to
be out of reset.
Refactor the code so we always wait for the PHY after the core has been
deasserted, since this works for both artpec6 and artpec7.

Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>