OvmfPkg/BaseCachingPciExpressLib: Migrate BaseCachingPciExpressLib

OvmfPkg/BaseCachingPciExpressLib: Migrate BaseCachingPciExpressLib

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>