initramds-framework: add shutdown hook for udev

initramds-framework: add shutdown hook for udev

In cases where other initramfs modules need to rely on
udev running (ie in my case I have to load firmware on
a device that is slow to start) there needs to be a way
to keep it running during the lifecycle of the initramfs
but still be shut down before swith_root is called.  I
added a  module_pre_hook that will shut down udev before
the finish module is called.

(From OE-Core rev: ce690659ef797bd26dc2be59167aa01744841510)

Signed-off-by: Ian Reinhart Geiser <igeiser@devonit.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>