asahi: Implement scratch
First pass at implementing scratch. Passes dEQP-GLES2/3/31 (which do use scratch to an extent after these changes) on G13G and G14C, others untested (G13X in particular needs testing, since the core/cluster ID bit assignments might not match, and also GxxD might have the die ID somewhere non-adjacent).
Edited by Asahi Lina