PCI: mvebu: Fix support for DEVCAP2, DEVCTL2 and LNKCTL2 registers on emulated bridge

Armada XP and new hardware supports access to DEVCAP2, DEVCTL2 and LNKCTL2
configuration registers of PCIe core via PCIE_CAP_PCIEXP. So export them
via emulated software root bridge.

Pre-XP hardware does not support these registers and returns zeros.

Link: https://lore.kernel.org/r/20211125124605.25915-16-pali@kernel.org
Fixes: 1f08673e

 ("PCI: mvebu: Convert to PCI emulated bridge config space")
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>