etnaviv: blt: blit with the original format when possible

etnaviv: blt: blit with the original format when possible

This fixes BGR565 blit: currently BGRA444 is used for the blit, but with
swizzles from the original BGR565 format, so the 4 alpha bits are set to 1.
We can't just use the swizzle from the 'compatible' format, since there are
cases where BGR<->RGB swap needs to happen.

We can avoid all this trouble by using the original formats and only
falling back to the 'compatible' format when we need to.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>