Edk2Setup.bat: Fix build errors from VS tools PREFIX ENV missing

Edk2Setup.bat: Fix build errors from VS tools PREFIX ENV missing

BaseTools/set_vsprefix_envs.bat is introduced for setting the PREFIX ENV
of VS tools in tools_def.template.
For example:

DEFINE VS2015_BIN      = ENV(VS2015_PREFIX)Vc\bin
DEFINE VS2015_DLL      = ENV(VS2015_PREFIX)Common7\IDE;DEF(VS2015_BIN)
DEFINE VS2015_BINX64   = DEF(VS2015_BIN)\x86_amd64

The issue is EdkSetup.bat calls BaseTools\set_vsprefix_envs.bat but
Edk2Setup.bat does not.

Edk2Setup.bat should call BaseTools/set_vsprefix_envs.bat  to set up the
PREFIX ENV of VS tools.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Cinnamon Shia <cinnamon.shia@hpe.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>