Add cpuinfo support for the new MicroBlaze option permitting userspace
(unprivileged) access to the streaming instructions (FSL / AXI-stream).

Emit a noisy warning at bootup if this is enabled, because bad user code
can potentially lockup the CPU.
Signed-off-by: NJohn A. Williams <john.williams@petalogix.com>
Signed-off-by: NMichal Simek <monstr@monstr.eu>