BaseTools: Update toolsetup.bat to support the case without EDK_TOOLS_BIN

BaseTools: Update toolsetup.bat to support the case without EDK_TOOLS_BIN

When EDK_TOOLS_BIN is not set, %EDK_TOOLS_PATH%\Bin\Win32 will be used as the
binary tool directory. But, %EDK_TOOLS_PATH%\Bin\Win32 may not exist. On this
case, toolsetup.bat should continue to do the other setting, such VS tool
chain and tool conf file copy.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>