s390x/pci: factor out endianess conversion

s390x/pci: factor out endianess conversion

There are two places where the same endianness conversion
is done.
Let's factor this out into a static function.

Note that the conversion must always be done for data in a register:

The S390 BE guest converted date to le before issuing the instruction.

After interception in a BE host:
ZPCI VFIO using pwrite must make the conversion back for the BE kernel.
Kernel will do BE to le translation when loading the register for the
real instruction.

After interception in a le host:
TCG stores a BE register in le, swapping bytes.
But since the data in the register was already le it is now BE
ZPCI VFIO must convert it to le before writing to the PCI memory.

In both cases ZPCI VFIO must swap the bytes from the register.

Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Reviewed-by: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
Message-Id: <1512046530-17773-2-git-send-email-pmorel@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>