panfrost/midgard: Handle pure int formats

panfrost/midgard: Handle pure int formats

I'm not sure I'm totally comfortable with this, but conceptually neither
float nor pure-int formats require any format conversion, except size
conversion. Going from a shaderable format (fp32 or i16, for instance)
into a blendable format (fp16) is a separate question, one we can defer
momentarily while we're not interested in actually blending.

As an aside, I'd be fascinated by an integer-based blending
implementation.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>