aarch64.risu: add C3.6.26 Floating-point data-processing (2 source)

this adds C3.6.26, including

FMUL (scalar), FNMUL, FDIV (scalar), FADD (scalar), FSUB (scalar),
FMAX (scalar), FMIN (scalar), FMAXNM (scalar), FMINNM (scalar)

Signed-off-by: Claudio Fontana <claudio.fontana@linaro.org>