drm/i915: Add Guc/HuC firmware details to error state

Include GuC and HuC firmware details in captured error state
to provide additional debug information. To reuse existing
uc firmware pretty printer, introduce new drm-printer variant
that works with our i915_error_state_buf output. Also update
uc firmware pretty printer to accept const input.

v2: don't rely on current caps (Chris)
    dump correct fw info (Michal)
v3: simplify capture of custom paths (Chris)
v4: improve 'why' comment (Joonas)
    trim output if no fw path (Michal)
    group code around uc error state (Michal)
v5: use error in cleanup_uc (Michal)

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171026173657.49648-1-michal.wajdeczko@intel.com


[ickle: allow printing uc_fw after allocation failure]
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>