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.

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

 * 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 <>
Reviewed-by: Kenneth Graunke <>
Acked-by: Jason Ekstrand <>
25 jobs for !338 with iris-fp64 in 34 minutes and 10 seconds (queued for 1 minute and 25 seconds)
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