This is a cleanup.
Old gs LDS layout: [es outputs][gs outputs][scratch]
Old nogs LDS layout: [xfb/cull][scratch]
New gs LDS layout: [es outputs][scratch|gs outputs]
New nogs LDS layout: [scratch|xfb/cull]
The LDS scratch is moved to the beginning of the preceding buffer in LDS,
while the addresses in that LDS buffer are offset by the scratch size.
It effectively merges the LDS scratch with the preceding buffer in LDS.
Thanks to that, we no longer need the ngg_scratch ABI and the offset
in a user SGPR.
The lowering passes now return the LDS scratch size, which is used
by the drivers to determine the final LDS size.
The ngg_lds_layout SGPR is now unused without GS in RADV.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35352>