radeonsi: move 2nd-shader descriptor pointers into s[0:1]

radeonsi: move 2nd-shader descriptor pointers into s[0:1]

If 32-bit pointers are supported, both pointers can be moved into s[0:1]
and then ESGS has exactly the same user data SGPR declarations as VS.

If 32-bit pointers are not supported, only one pointer can be moved into
s[0:1]. In that case, the 2nd pointer is moved before TCS constants,
so that the location is the same in HS and GS.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>