There are only three unused format flags left. I will soon submit changes
which add four more format flags.

I've noticed that format flags generally fall into two groups:

* The first group consists of flags describing the content of a pixel
  format, e.g. whether or not this is a depth format, or whether this is
  a blocked format. These flags are the same for all resource types.
* The second group consists of flags describing capabilities of the
  implementation with this format. These can and do vary by resource
  type.

Only the second group needs to be stored per-resource-type.
Signed-off-by: Chip Davis <cdavis5x@gmail.com>