On non-EFI systems, it wasn't possible to test the platform firmware
loader because it will have never set "checked_fw" during __init.
Instead, allow the test code to override this check. Additionally split
the declarations into a private header file so it there is greater
enforcement of the symbol visibility.

Fixes: 548193cb ("test_firmware: add support for firmware_request_platform")
Cc: stable@vger.kernel.org
Acked-by: NScott Branden <scott.branden@broadcom.com>
Signed-off-by: NKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200724213640.389191-2-keescook@chromium.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>