drm/i915: kill resource streamer support

drm/i915: kill resource streamer support

After disabling resource streamer on ICL (due to it actually not
existing there), I got feedback that there have been some experimental
patches for mesa to use RS years ago, but nothing ever landed or shipped
because there was no performance improvement.

This removes it from kernel keeping the uapi defines around for
compatibility.

v2: - re-add the inadvertent removal of CTX_CTRL_INHIBIT_SYN_CTX_SWITCH
    - don't bother trying to document removed params on uapi header:
      applications should know that from the query.
      (from Chris)

v3: - disable CTX_CTRL_RS_CTX_ENABLE istead of removing it
    - reword commit message after Daniele confirmed no performance
      regression on his machine
    - reword commit message to make clear RS is being removed due to
      never been used
v4: - move I915_EXEC_RESOURCE_STREAMER to __I915_EXEC_ILLEGAL_FLAGS so
      the check on ioctl() is made much earlier by
      i915_gem_check_execbuffer() (suggested by Tvrtko)

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180803232443.17193-1-lucas.demarchi@intel.com