iommu: msm_iommu_sec: fix some overeager cache maintenance

In general, we must do some cache maintenance when sharing buffers with
TZ since our caches are not shared with TZ.  Specifically:

    (1) If we put some data into a buffer then share it with TZ for
        reading, the buffer must be flushed before sending it to TZ.

    (2) If TZ puts some data in a buffer for us to read, the buffer must
        be invalidated after receiving it from TZ.

In msm_iommu_sec_ptbl_map we are currently doing some cache maintenance
incorrectly.  We are invalidating a buffer that we shared with TZ even
though we're not reading from the buffer.  We're also flushing way more
than we need to.  We're only sharing a single buffer of size
sizeof(phys_addr_t) with TZ but we're flushing the size of the IOMMU
mapping (which could be anything up to 2^sizeof(size_t)).

Remove the unnecessary invalidate and only flush the size of the buffer
being shared, nothing more.

Change-Id: I46d2d95319364d197ae530001851ab819a6eb6fa
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>