v3dv: don't swap RB channels when copying images to buffers

v3dv: don't swap RB channels when copying images to buffers

We don't need to do this, since we are just copying. Also, we are not
swapping on the store, so doing it on the load would be incorrect.
This gets the prime blit present path in WSI common to render R/B
channels correctly after blitting from the BGRA image to the linear
buffer for display output.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>