ACPICA: EFI/EDK2: Cleanup to enable /WX for MSVC builds

ACPICA commit a7c6d65a5dab20b1e191c197e09af337fc54b341

/WX turns warning into fatal erros for MSVC builds. We need /WX- during
EDK2 porting to allow agile development.

Now it is time to enable /WX and some explicit type conversion cleanups
are required for enabling /WX. Lv Zheng.

Link: https://github.com/acpica/acpica/commit/a7c6d65a


Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>