SecurityPkg: Update PlatformSecureLibNull with PCD to get physical presence.

SecurityPkg: Update PlatformSecureLibNull with PCD to get physical presence.

This is an incompatible change. It uses PcdUserPhysicalPresence value instead
of hard code TRUE. Because PcdUserPhysicalPresence default value is FALSE,
this patch changes UserPhysicalPresent() return value from TRUE to FALSE.

From Security point, it is not safe to always return TRUE. If user wants this
behavior, he can still configure PcdUserPhysicalPresence value to TRUE in
the platform DSC file.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Giri P Mudusuru <giri.p.mudusuru@intel.com>