It's a bit hard to exactly map our implementation to the limits
described by Vulkan.  The bindless surface handle in the extended
message descriptors is 20 bits and it's an index into the table of
RENDER_SURFACE_STATE structs that starts at bindless surface base
address.  This means that we can have at must 1M surface states
allocated at any given time.  Since most image views take two
descriptors, this means we have a limit of about 500K image views.

However, since we allocate surface states at vkCreateImageView time,
this means our limit is actually something on the order of 500K image
views allocated at any time.  The actual limit describe by Vulkan, on
the other hand, is a limit of how many you can have in a descriptor set.
Assuming anyone using 1M descriptors will be using the same image view
twice a bunch of times (or a bunch of null descriptors), we can safely
advertise a larger limit.  1M is what's required by D3D12, so let's
advertise that.

Closes: mesa/mesa#3335


Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <mesa/mesa!7180>