AcpiDebugFeaturePkg: Included modules are mutually exclusive

The DXE and SMM versions of AcpiDebug perform the same task and
are therefore mutually exclusive. Including both modules results in a
duplicate ACPI table, resulting in the feature not working at all.

Therefore, add a new PCD to determine which module will be included.
Now, either version successfully write to the debug buffer.

Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Cc: Isaac Oram <isaac.w.oram@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Eric Dong <eric.dong@intel.com>
Signed-off-by: Benjamin Doron <benjamin.doron00@gmail.com>
Reviewed-by: Isaac Oram <isaac.w.oram@intel.com>