OvmfPkg: resolve PcdLib for all PEIMs individually

OvmfPkg: resolve PcdLib for all PEIMs individually

Currently the default (module type independent) PcdLib resolution is to
BasePcdLibNull.inf, which is inherited by all PEIMs. In the next patch,
we'll flip the PEIM default resolution to PeiPcdLib.inf, but in order to
keep that patch both correct and simple to review, we should spell out the
Null resolution for those two PEIMs (ReportStatusCodeRouterPei and
StatusCodeHandlerPei) that are now the only ones that don't specify an
explicit resolution.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>