target/ppc: Moved XVTSTDC[DS]P to decodetree

target/ppc: Moved XVTSTDC[DS]P to decodetree

Moved XVTSTDCSP and XVTSTDCDP to decodetree an restructured the helper
to be simpler and do all decoding in the decodetree (so XB, XT and DCMX
are all calculated outside the helper).

Obs: The tests in this one are slightly different, these are the sum of
these instructions with all possible immediate and those instructions
are repeated 10 times.

xvtstdcsp:
rept    loop    master             patch
8       12500   2,76402100         2,70699100 (-2.1%)
25      4000    2,64867100         2,67884100 (+1.1%)
100     1000    2,73806300         2,78701000 (+1.8%)
500     200     3,44666500         3,61027600 (+4.7%)
2500    40      5,85790200         6,47475500 (+10.5%)
8000    12     15,22102100        17,46062900 (+14.7%)

xvtstdcdp:
rept    loop    master             patch
8       12500   2,11818000         1,61065300 (-24.0%)
25      4000    2,04573400         1,60132200 (-21.7%)
100     1000    2,13834100         1,69988100 (-20.5%)
500     200     2,73977000         2,48631700 (-9.3%)
2500    40      5,05067000         5,25914100 (+4.1%)
8000    12     14,60507800        15,93704900 (+9.1%)

Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20221019125040.48028-11-lucas.araujo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>