target/arm: Set S and PTW in 64-bit PAR format

target/arm: Set S and PTW in 64-bit PAR format

In do_ats_write() we construct a PAR value based on the result
of the translation.  A comment says "S2WLK and FSTAGE are always
zero, because we don't implement virtualization".
Since we do in fact now implement virtualization, add the missing
code that sets these bits based on the reported ARMMMUFaultInfo.

(These bits are named PTW and S in ARMv8, so we follow that
convention in the new comments in this patch.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20181016093703.10637-2-peter.maydell@linaro.org