BaseTools: Improve GetDependencyList function

BaseTools: Improve GetDependencyList function

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2102

GetDependencyList get the header file via
re.findall in the whole header file.

This patch is to pre-process the header file and
to feed the shorter string to re.findall.

This patch is to improve GetDependencyList() efficiency

Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>