nvc0: restore image binding on RGB10A2, remove from BGR10A2

nvc0: restore image binding on RGB10A2, remove from BGR10A2

Fixes a bunch of new CTS pbo tests that use those as an output format,
which the state tracker converts into buffer image writes.

No part of the driver is ready for BGR10A2. It could probably be enabled
on Maxwell+, but seems unnecessary. This error was introduced when
flipping the displayable bit on those formats, which accidentally also
moved the image bit.

Fixes: e1a70aed10d (nv50,nvc0: mark ABGR format as displayable instead of ARGB format)
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>