drm/i915/uc: Update drawing for firmware layout

Sphinx was rendering firmware layout as html table, but since
we want to add sizes relations switch to plain text graphics.

v2: also update text and do it before move (Daniele)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190725141308.24660-2-michal.wajdeczko@intel.com