drm/i915/lrc: move lrc_get_runtime() to intel_lrc.c

Move the static inline next to the only caller.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220214173810.2108975-1-jani.nikula@intel.com