drm/i915/tgl: s/TGL/TIGERLAKE for platform/subplatform defines

Follow consistent naming convention. Replace TGL with
TIGERLAKE.Replace IS_TGL_DISPLAY_STEP with
IS_TIGERLAKE() && IS_DISPLAY_STEP().

v2:
- s/TGL/tgl in the subject prefix(Anusha)

v3:
- Unrolled wrapper IS_TGL_DISPLAY_STEP and Replace
- Replace IS_PLATFORM && DISPLAY_STEP (Jani/Tvrtko).

v4:
- Removed unused macros

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/20230801135344.3797924-10-dnyaneshwar.bhadane@intel.com