Move BaseCachingPciExpressLib library from ArmVirtPkg to under OvmfPkg.
RISC-V Virt platform can leverage the same library to access PCI Express
registers through PCI Express base address set in PcdPciExpressBaseAddress
and cached in a global variable.
Cc: Daniel Schaefer <daniel.schaefer@hpe.com> Cc: Sunil V L <sunilvl@ventanamicro.com> Cc: Jiewen Yao <jiewen.yao@intel.com> Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Abner Chang <abner.chang@hpe.com> Acked-by: Ard Biesheuvel <ardb@kernel.org>