gpm: run autogen.sh as PRE_CONFIGURE step

Move the GPM_RUN_AUTOGEN to be a PRE_CONFIGURE step because this step
depends on the dependancies being built. If it is a POST_PATCH step
the dependencies won't be built and the GPM_RUN_AUTOGEN step will fail
(if the host doesn't have autotools).

Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>