OvmfPkg: Modify QemuFwCfgLib to use new IoLib class library

OvmfPkg: Modify QemuFwCfgLib to use new IoLib class library

The Fifo routines from the QuemuFwCfgLib library have been ported
to the new BaseIoLibIntrinsic (IoLib class) library.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Leo Duran  <leo.duran@amd.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>