BaseTools/PatchCheck.py: Add LicenseCheck

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2691


For files to be added to the tree, this feature will check
whether it has BSD plus patent license. If not, licenses listed in
Readme are also accepted but warning will be reported.
Otherwise, it should be error.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Yuwei Chen <yuwei.chen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>