BaseTools: Fix the issue caused by tostring() removal on Py39

BaseTools: Fix the issue caused by tostring() removal on Py39

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3136

Python 3.9 remove the array.array.tostring and
array.array.fromstring() function. This patch
is to use other method to replace tostring() and
fromstring()

Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Cc: Mingyue Liang <mingyuex.liang@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>