drm/i915: Remove the module parameter 'fastboot'

By default fastboot is enabled on all Display 9+ platforms and disabled
on older platforms. Its not necessary to retain this as a module
parameter.

Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230926091157.635438-1-arun.r.murthy@intel.com