Extend Blitter::fastClear(), which is based on memset() instead of using
Reactor routines, to also handle D32_SFLOAT and S8_UINT formats.

Benchmark results:

Run on (48 X 2594 MHz CPU s)
CPU Caches:
  L1 Data 32 KiB (x24)
  L1 Instruction 32 KiB (x24)
  L2 Unified 256 KiB (x24)
  L3 Unified 30720 KiB (x2)
--------------------------------------------------------------------------
Benchmark                                Time             CPU   Iterations
--------------------------------------------------------------------------
(LLVM, before)
ClearImage/VK_FORMAT_D32_SFLOAT       3.74 ms        0.016 ms         1000

(LLVM, after)
ClearImage/VK_FORMAT_D32_SFLOAT       1.08 ms        0.044 ms        10000

(Subzero, before)
ClearImage/VK_FORMAT_D32_SFLOAT       4.51 ms        0.063 ms         1000

(Subzero, after)
ClearImage/VK_FORMAT_D32_SFLOAT      0.963 ms        0.040 ms         7467

Bug: b/159455503
Change-Id: Ib1b0ad38417c516267d6addd835076a933e22dba
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/45888
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>