freedreno/ir3: Simpify the immediates from an array of vec4 to array of dwords.

freedreno/ir3: Simpify the immediates from an array of vec4 to array of dwords.

We usually had to split the idx/swiz out of the dword index anyway.  Note
that incidentally, immediates_size now increments in vec4s instad of
4*vec4s.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5990>