MdeModulePkg VariableInfo: Always consider RT DXE and SMM stats

MdeModulePkg VariableInfo: Always consider RT DXE and SMM stats

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2220

The current VariableInfo application only checks for variable
statistics from SMM if the variable information entries are
not present in the UEFI System Configuration table as published
by the DXE UEFI variable driver (VariableRuntimeDxe).

This change first checks for variable information entries in the
UEFI System Configuration but always checks for entries in SMM
as well. If the SMM variable driver is not present, an instance of
EFI_SMM_VARIABLE_PROTOCOL will not be found and the search for
SMM variable statistics will be aborted (an SW SMI to get variable
statistics will not be triggered).

In the case variable statistics are provided by both a Runtime DXE
driver (e.g. VariableSmmRuntimeDxe) and a SMM driver (VariableSmm),
this change will clearly identify statistics from each respective
driver.

Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Michael Kubacki <michael.a.kubacki@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Acked-by: Hao A Wu <hao.a.wu@intel.com>