target/ppc: Move floating-point arithmetic instructions to decodetree.

target/ppc: Move floating-point arithmetic instructions to decodetree.

This patch moves the below instructions to decodetree specification :

    f{add, sub, mul, div, re, rsqrte, madd, msub, nmadd, nmsub}[s][.] : A-form
    ft{div, sqrt}                                                     : X-form

With this patch, all the floating-point arithmetic instructions have been
moved to decodetree.
The changes were verified by validating that the tcg ops generated by those
instructions remain the same, which were captured with the '-d in_asm,op' flag.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Chinmay Rath <rathc@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>