s390/pci: enforce fmb page boundary rule

The function measurement block must not cross a page boundary. Ensure
that by raising the alignment requirement to the smallest power of 2
larger than the size of the fmb.

Fixes: d0b08853 ("s390/pci: performance statistics and debug infrastructure")
Cc: stable@vger.kernel.org # v3.8+
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>