UefiCpuPkg: Add BaseRiscV64CpuTimerLib library

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4076



Add the RISC-V instance of the TimerLib.

This is mostly copied from
edk2-platforms/Silicon/RISC-V/ProcessorPkg/Library/RiscVTimerLib

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Daniel Schaefer <git@danielschaefer.me>
Cc: Abner Chang <abner.chang@amd.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: Ray Ni <ray.ni@Intel.com>