drm/i915/tgl: stop using ERROR_GEN6 and DONE_REG

These registers have been removed on gen12.

v2: merge common branch for IS_GEN_RANGE(i915, 6, 11)

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190730180407.5993-3-lucas.demarchi@intel.com