anv: fix some multisample line_wide CTS tests

After spending some time trying to understand how line rasterization and
multisampling work, I am convinced that I know even less now than I did
before.

Brute forcing my way through it, I found that the respective tests pass
if we set DXMultisampleRasterizationEnable to false, but that then
breaks a bunch of other tests under dEQP-VK.pipeline.multisample.*.
A compromise is reached by setting this bit based on the requested line
width, and since this doesn't seem to be breaking anything else that I
noticed, I'm happy to pretend it's a success.

v2: Take values under 1.0 into account (Jason)

Closes #2833
Fixes dEQP-VK.rasterization.interpolation_multisample_*_bit.*lines_wide
33 jobs for !10420 with lines_wide in 8 seconds (queued for 4 seconds)
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