drm/i915/dmc: abstract GPU error state dump

Only intel_dmc.c should be accessing dmc details directly.

Need to add an i915_error_printf() stub for
CONFIG_DRM_I915_CAPTURE_ERROR=n.

v2: Add the stub (kernel test robot <lkp@intel.com>)

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com> # v1
Link: https://patchwork.freedesktop.org/patch/msgid/20220330113417.220964-1-jani.nikula@intel.com