drm/i915: Use str_yes_no()

Remove the local yesno() implementation and adopt the str_yes_no() from
linux/string_helpers.h.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220225234631.3725943-1-lucas.demarchi@intel.com