drm/i915: Make the intel_device_info structure kept in dev_priv writable

drm/i915: Make the intel_device_info structure kept in dev_priv writable

Turns out it'd be nice to change some device information at run-time or simply
have some code to fill in the info struct instead of having to declare the
values in 30+ structures.

What prompted this change is handling fused out display/pipe and tweaking
num_pipes at run-time, but I'm quite sure we'll find other flags/limits to
stick into dev_priv->info.

Most of the changes were done with a sed:
sed -i -e 's/dev_priv->info->/dev_priv->info./g' drivers/gpu/drm/i915/*[ch]

with a few tweaks to make it all work:
- Change the field definition in struct drm_i915_private
- adjust i915_dump_device_info()
- adjust i915_driver_load()
- adjust the INTEL_INFO() macro

v2: cast the info pointer returned by INTEL_INFO() to be const to catch
    uses that would modify the structure post-initialization.
    (Ville Syrjälä)

v3: Redo the patch onto latest drm-nightly,
    Keep the info field const to catch post initialization writes
    instead of the v2 solution,
    Use a direct structure copy for the initial info initialization to
    use the compiler type safety (Ville Syrjälä)

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> (for v2)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> (for v2)
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>