pseries: Fix initialization of sPAPREnvironment structure

Since we added PCI support to the pseries machine, we include a qlist of
PCI host bridges in the sPAPREnvironment structure.  However this list
was never properly initialized it.  Somehow we got away with this until
some other recent change broke it, and we now segfault immediately on
startup.

This patch adds the required QLIST_INIT(), and while we're at it makes sure
we initialize the rest of the sPAPREnvironment structure to 0, to avoid
future nasty surprises.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
