drm/i915/rkl: s/RKL/ROCKETLAKE for platform/subplatform defines

Follow consistent naming convention. Replace RKL with
ROCKETLAKE.Replace IS_RKL_GRAPHICS_STEP with
IS_ROCKETLAKE && IS_DISPLAY_STEP.

v2:
- s/RKL/rkl in the subject prefix(Anusha)

v3:
- Unrolled wrapper IS_RKL_DISPLAY_STEP.
- Replace IS_PLATFORM && IS_DISPLAY_STEP (Jani/Tvrtko)

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230801135344.3797924-8-dnyaneshwar.bhadane@intel.com