st/mesa: add support for lowering fp64/int64 for nir drivers

This might enough for iris and possible r600 (when it gets NIR)

This appears to work for iris.

v2:
 * change cap return so DOUBLES == 2 means sw emu

v3:
 * Refactor using int64/doubles lowering options which were added
   into nir options
 * Remove DOUBLES == 2 added in v2

[jordan: Remove "2" value on PIPE_CAP_DOUBLES]
[jordan: Use lowering options added to nir options]
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
25 jobs for !338 with iris-fp64 in 34 minutes and 10 seconds (queued for 1 minute and 25 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #149350
containers:ubuntu

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  Build+Test
passed #149365
build:make-gallium-drivers-other

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build:make-gallium-drivers-radeonsi

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build:make-gallium-drivers-swr

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build:make-gallium-st-clover-llvm-39

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build:make-gallium-st-clover-llvm-4

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build:make-gallium-st-clover-llvm-5

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build:make-gallium-st-clover-llvm-6

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build:make-gallium-st-clover-llvm-7

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build:make-gallium-st-other

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build:make-loader-classic-dri

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build:make-vulkan

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build:meson-gallium-clover-llvm5

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build:meson-gallium-clover-llvm6

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build:meson-gallium-clover-llvm7

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passed #149356
build:meson-gallium-drivers-other

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build:meson-gallium-radeonsi

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passed #149360
build:meson-gallium-st-other

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passed #149354
build:meson-gallium-swr

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build:meson-glvnd

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passed #149352
build:meson-loader-classic-dri

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build:meson-vulkan

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build:scons-llvm

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build:scons-nollvm

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build:scons-swr

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