SecurityPkg: Don't build AuthVariableLib for EBC arch

SecurityPkg: Don't build AuthVariableLib for EBC arch

EBC build failure is caused by d7a09cb86a0416c099fa3a9e0fbe2c8f399b28de.
It changes MAX_UINTN definition as below. AuthVariableLib uses MAX_UINTN
in the global data initialization. New style has >> operator, and not
supported by EBC compiler. The fix is not to build AuthVariableLib for EBC.

#define MAX_UINTN  ((UINTN) ~0)
==>
#define MAX_UINTN  ((UINTN)(~0ULL >> (64 - sizeof (INTN) * 8)))

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Chao Zhang <chao.b.zhang@intel.com>