panfrost: Support float/vec2/vec3 attributes

Previously, we had hard-coded the number of components to equal 4 (vec4), due to mysterious issues occurring when the count was less than 4. Further investigation shows that not only the component count needs updating but also the magic value in the unknown1 field. That field still needs to be further decoded - I suspect it controls how extra components are padded out - but for now, this patch allows these attributes to work at all.

This enables Sway to render.