linux-imx

s390/pci: add locking for fmb access

Function measurement can be toggled at runtime. Make sure that
all access to the fmb is protected via a mutex.

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