radeonsi: get rid of img/buf/sampler descriptor preloading (v2)

radeonsi: get rid of img/buf/sampler descriptor preloading (v2)

26011 shaders in 14651 tests
Totals:
SGPRS: 1251920 -> 1152636 (-7.93 %)
VGPRS: 728421 -> 728198 (-0.03 %)
Spilled SGPRs: 16644 -> 3776 (-77.31 %)
Spilled VGPRs: 369 -> 369 (0.00 %)
Scratch VGPRs: 1344 -> 1344 (0.00 %) dwords per thread
Code Size: 36001064 -> 35835152 (-0.46 %) bytes
LDS: 767 -> 767 (0.00 %) blocks
Max Waves: 222221 -> 222372 (0.07 %)
Wait states: 0 -> 0 (0.00 %)

v2: merge codepaths where possible

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