This commit adds some algebraic properties to the metadata of each opcode
in NIR.  In particular, you now know, just from the metadata, if a given
opcode is commutative or associative.  This will be useful for algebraic
transformation passes that want to be able to match a + b as well as b + a
in one go.

v2: Make algebraic properties all caps.  This was more consistent with the
    intrinsics flags and seems better for flags in general.

    Also, the enums are now declared with (1 << n) rather then hex values.

v3: fmin and fmax technically aren't commutative or associative.  Things
    get funny when one of the arguments is a NaN.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>