OvmfPkg/RiscVVirt: Add VirtNorFlashPlatformLib library

Qemu NOR flash driver needs this library. Add this
library for RISC-V leveraged from SbsaQemu.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Abner Chang <abner.chang@amd.com>
Reviewed-by: Andrei Warkentin <andrei.warkentin@intel.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>