pci: zynqmp: Fix the pcireg base

pci: zynqmp: Fix the pcireg base

The pcireg base is not assigned to any address, reading the
pcireg base with PS_LINKUP_OFFSET which is incorrect and
giving random values. So update the pcireg base from
devicetree so that we can read the valid PCIE link status
and PHY ready status.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Link: https://lore.kernel.org/r/20250516092314.939424-1-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>