vc4: Add support for swizzles of 32 bit float vertex attributes.

vc4: Add support for swizzles of 32 bit float vertex attributes.

Some tests start working (useprogram-flushverts, for example) due to
getitng the right vertices now.  Some that used to pass start failing with
memory overflow during binning, which is weird (glsl-fs-texture2drect).
And a couple stop rendering correctly (glsl-fs-bug25902).

v2: Move the attribute format setup in the key from after search time to
    before the search.
v3: Fix reading of attributes other than position (I forgot to respect
    attr and stored everything in inputs 0-3, i.e. position).