Platform/Intel: Dynamic NUMBER_OF_PROCESSORS in build.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1913



To improve build performance by default the maximum
processors should be used for building.
NUMBER_OF_PROCESSORS in build.cfg is set to 0 so
BaseTools can utilize maximum processors for build.

Test: tried NUMBER_OF_PROCESSORS 0 and 1 cases and
      confirmed the build time is half with 0 case.

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>