v3d: Use driconf to expose non-MSAA texture limits for Xorg.

The V3D 4.2 HW has a limit to MSAA texture sizes of 4096.  With non-MSAA,
we can go up to 7680 (actually probably 8138, but that hasn't been
validated by the HW team).  Exposing 7680 in X11 will allow dual 4k displays.
10 jobs for !779 with v3d-maxsize in 10 minutes and 19 seconds (queued for 19 seconds)
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Status Job ID Name Coverage
  Containers Build
passed #295638
debian

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  Build+Test
passed #295640
meson-clang

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passed #295644
meson-clover

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passed #295643
meson-main

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passed #295639
meson-swr-glvnd

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passed #295645
meson-vulkan

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passed #295647
scons-llvm

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passed #295646
scons-nollvm

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passed #295641
scons-swr

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passed #295642
scons-win64

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