firmware_class: make firmware caching configurable

Because firmware caching generates uevent messages that are sent over
a netlink socket, it can prevent suspend on many platforms.  It's
also not always useful, so make it a configurable option.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: Tim Murray <timmurray@google.com>
Cc: Venkata Narendra Kumar Gutta <vnkgutta@codeaurora.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20191113225429.118495-1-salyzyn@android.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>