drm: increase DRM_OBJECT_MAX_PROPERTY to 24

Before Kernel 3.5, no one was checking for the return value of
drm_connector_attach_property, so we never noticed that we were unable
to create some properties. Commit "drm: WARN() when
drm_connector_attach_property fails" added a WARN when we fail to
create a property, and the transition from "connector properties" to
"object properties" changed the warning message a little bit.

On i915 machines with many TV connectors we hit the maximum number of
properties (since each TV connector uses a lot of properties), so we
get a few backtraces in our logs. This commit increases the maximum
number of properties to 24 hoping we'll have enough room for
everybody.

Chris suggested that we convert this code to "lists", but I believe
this conversion can come after we make sure people's dmesgs are not
spammed by our driver.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reported-by: Dave Jones <davej@redhat.com>
Tested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>