radeonsi: put up to 5 VBO descriptors into user SGPRs

radeonsi: put up to 5 VBO descriptors into user SGPRs

gfx6-8: 1 VBO descriptor in user SGPRs
gfx9-10: 5 VBO descriptors in user SGPRs

We no longer pull up to 5 VBO descriptors from GTT when SDMA is disabled.

Totals from affected shaders:
SGPRS: 1110528 -> 1170528 (5.40 %)
VGPRS: 952896 -> 951936 (-0.10 %)
Spilled SGPRs: 83 -> 61 (-26.51 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 23766296 -> 22843920 (-3.88 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 179344 -> 179344 (0.00 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>