xilinx: Remove the legacy property "#stream-id-cells"

"#stream-id-cells" was being used with "mmu-masters" for Xen specific
device trees.
With Xen commit 2278d2cbb0b7c1b48b298c6c4c6a7de2271ac928 (Link below)
Xen is able to support smmu bindings in both formats ie :
1. Using iommus (linux format)
2. Using mmu-masters (legacy format).

Thus, "#stream-id-cells" which was used for the legacy format, can be
removed as Xen can use smmu bindings in linux format.

Link: https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg101649.html


Signed-off-by: Ayan Kumar Halder <ayankuma@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/1e062acb233dee47cd7dd2429cb482132617cbc8.1655886415.git.michal.simek@amd.com