OvmfPkg: Update dsc to use IoLib from BaseIoLibIntrinsicSev.inf

OvmfPkg: Update dsc to use IoLib from BaseIoLibIntrinsicSev.inf

When SEV is enabled then we must unroll the rep String I/O instructions.

The patch updates dsc file to use SEV version of IoLib inf. The main
difference between BaseIoLibIntrinsic.inf and BaseIoLibIntrinsicSev.inf
is, SEV version checks if its running under SEV enabled guest, If so
then it unroll the String I/O (REP INS/OUTS) otherwise fallbacks to
rep ins/outs.

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>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>