firmware: replace #ifdef over FW_OPT_FALLBACK with function checks

firmware: replace #ifdef over FW_OPT_FALLBACK with function checks

Its not easy to follow the logic behind making FW_OPT_FALLBACK map
to an existing flag only if a kernel configuration option was set.
Its much easier to retpresent what was intended with function helpers
which make it clear that if CONFIG_FW_LOADER_USER_HELPER_FALLBACK is
set we force running the fallback mechanism unless a caller specifically
never wants to run it, such as request_firmware_direct().

Prior and after this change we upkeep the tradition:

CONFIG_FW_LOADER_USER_HELPER_FALLBACK
	request_firmware() force fallback
	request_firmware_into_buf() force fallback
	request_firmware_nowait() force fallback
	request_firmware_direct() always ignore fallback

!CONFIG_FW_LOADER_USER_HELPER_FALLBACK
	request_firmware() ignore fallback
	request_firmware_into_buf() ignore fallback
	request_firmware_nowait() depends on uevent flag
	request_firmware_direct() always ignore fallback

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>