Make flatview_access_valid() take a MemTxAttrs argument

Make flatview_access_valid() take a MemTxAttrs argument

As part of plumbing MemTxAttrs down to the IOMMU translate method,
add MemTxAttrs as an argument to flatview_access_valid().
Its callers now all have an attrs value to hand, so we can
correct our earlier temporary use of MEMTXATTRS_UNSPECIFIED.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180521140402.23318-10-peter.maydell@linaro.org