gen_msvs_(vcx)proj.sh: set yasm format explicitly

use win32/win64 instead of $(PlatformName) (Win32/x64) for compatibility
with yasm 1.3.0. both format types were available since at least 0.8.0

BUG=843

Change-Id: I7917620490d0663b118ff08b96d1e5dbccba3703
2 files changed