firmware: use helpers for setting up a temporary cache timeout

We only use the timeout for the firmware fallback mechanism
except for trying to set the timeout during the cache setup
for resume/suspend. For those cases, setting the timeout should
be a no-op, so just reflect this in code by adding helpers for it.

This change introduces no functional changes.

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