drm/i915/params: use generics for parameter free

Replace the __builtin_strcmp() if ladder with generics.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230118151800.3669913-3-jani.nikula@intel.com