target/ppc: Move VNEG[WD] to decodtree and use gvec

target/ppc: Move VNEG[WD] to decodtree and use gvec

Moved the instructions VNEGW and VNEGD to decodetree and used gvec to
decode it.

vnegw:
rept    loop    master             patch
8       12500   0,01053200         0,00548400 (-47.9%)
25      4000    0,01030500         0,00390000 (-62.2%)
100     1000    0,01096300         0,00395400 (-63.9%)
500     200     0,01472000         0,00712300 (-51.6%)
2500    40      0,03809000         0,02147700 (-43.6%)
8000    12      0,09957100         0,06202100 (-37.7%)

vnegd:
rept    loop    master             patch
8       12500   0,00594600         0,00543800 (-8.5%)
25      4000    0,00575200         0,00396400 (-31.1%)
100     1000    0,00676100         0,00394800 (-41.6%)
500     200     0,01149300         0,00709400 (-38.3%)
2500    40      0,03441500         0,02169600 (-37.0%)
8000    12      0,09516900         0,06337000 (-33.4%)

Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20221019125040.48028-5-lucas.araujo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>