risugen: change floating point randomization for aarch64
risugen: change floating point randomization for aarch64

generate "interesting" values for aarch64 as well,
in the same way as we do for ARM.

Also disable use of LD1 to load 4 regs at a time, for now,
and replace with LDP Qn, which loads only 2 regs at a time.
As LD1 is implemented and stable, we can switch back to use it.

Signed-off-by: Claudio Fontana <5fe97b97070bc75ff3c7a6b130e2dcc62cbb9b58@linaro.org>

hw-claudio/risu-aarch64,hw-claudio/risu-aarch64