drm/i915/psr: Move printing PSR mode to own function

intel_psr_status has grown and is about to grow even. Let's split it a bit
and move printing PSR mode to an own function.

v2: s/intel_psr_psr_mode/intel_psr_print_mode/

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240528114455.175961-5-jouni.hogander@intel.com