soft-fp64/fsat: Micro-optimize x >= 1 test

soft-fp64/fsat: Micro-optimize x >= 1 test

Results on the 308 shaders extracted from the fp64 portion of the OpenGL
CTS:

Tiger Lake and Ice Lake had similar results. (Tiger Lake shown)
total instructions in shared programs: 841590 -> 841332 (-0.03%)
instructions in affected programs: 121957 -> 121699 (-0.21%)
helped: 7
HURT: 0
helped stats (abs) min: 15 max: 54 x̄: 36.86 x̃: 41
helped stats (rel) min: 0.16% max: 0.33% x̄: 0.23% x̃: 0.18%
95% mean confidence interval for instructions value: -49.73 -23.98
95% mean confidence interval for instructions %-change: -0.29% -0.16%
Instructions are helped.

total cycles in shared programs: 6926828 -> 6923967 (-0.04%)
cycles in affected programs: 1038569 -> 1035708 (-0.28%)
helped: 7
HURT: 0
helped stats (abs) min: 128 max: 616 x̄: 408.71 x̃: 446
helped stats (rel) min: 0.18% max: 0.44% x̄: 0.29% x̃: 0.22%
95% mean confidence interval for cycles value: -571.72 -245.70
95% mean confidence interval for cycles %-change: -0.38% -0.19%
Cycles are helped.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4142>