s390/pci: cleanup function information block

Cleanup function information block used as a modify pci function
parameter. Change reserved members to be anonymous. Fix the size
of the struct and add proper alignment information. Also put the
FIB on the stack.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>