PCI: aardvark: Add support for PCI Bridge Subsystem Vendor ID on emulated bridge

PCI: aardvark: Add support for PCI Bridge Subsystem Vendor ID on emulated bridge

Register with Subsystem Device/Vendor ID is at offset 0x2c.

Export it via the emulated bridge to enable support for the Subsystem
Device/Vendor ID - by reading it in the PCI controller config space and
storing it in the emulated bridge control structures, so that it is
exposed in the respective PCI capability.

After this change Subsystem ID is visible in lspci output at line:

  Capabilities: [40] Subsystem

Link: https://lore.kernel.org/r/20220711225915.13896-1-pali@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>