drm/msm: add sudo flag to submit ioctl

This flags cause cmdstream to be executed from the ringbuffer (RB)
instead of IB1.  Normally not something you'd ever want to do, but
it is super useful for firmware debugging.

Hidden behind CAP_SYS_RAWIO and a default=n kconfig option which
depends on EXPERT (and has a suitably scary warning), to prevent
it from being used on accident.

Signed-off-by: Rob Clark <robdclark@gmail.com>