drm/i915: remove all IS_<PLATFORM>_GT<N>() macros

There aren't many users for the IS_<PLATFORM>_GT<N>() macros, and many
of them are in fact unused. Even among the users, the platform check is
often redundant. Just remove the macros.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240930124948.3551980-1-jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>