drm/i915: remove explicit CNL handling from i915_irq.c

Remove special handling of PORT_F in i915_irq.c and only do it for
DISPLAY_VER == 11.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210728215946.1573015-17-lucas.demarchi@intel.com