This new type exposes the additional precision offered by the
accumulator register and will be used in the next patch to implement the
functionality of the PLN instruction using a pair of MAD instructions.

One weird thing to note: align1 ternary instructions may only have an
accumulator in the dst or src1 normally, but when src0's type is :NF
the accumulator is read.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>