nir/spirv: implement ordered / unordered floating point comparisons properly

nir/spirv: implement ordered / unordered floating point comparisons properly

Besides the logical operation involved, these also require that we test if the
operands are ordered / unordered.

For ordered operations, both operands must be ordered (and they must pass the
conditional test) while for unordered operations it is sufficient if only one
of the operands is unordered (or they pass the logical test).

Fixes the following Vulkan CTS tests:

dEQP-VK.spirv_assembly.instruction.compute.opfunord.equal
dEQP-VK.spirv_assembly.instruction.compute.opfunord.greater
dEQP-VK.spirv_assembly.instruction.compute.opfunord.greaterequal
dEQP-VK.spirv_assembly.instruction.compute.opfunord.less
dEQP-VK.spirv_assembly.instruction.compute.opfunord.lessequal

v2: Fixed typo: s/nir_eq/nir_feq

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>