target/i386: convert SHLD/SHRD to new decoder

target/i386: convert SHLD/SHRD to new decoder

Use the same flag generation code as SHL and SHR, but use
the existing gen_shiftd_rm_T1 function to compute the result
as well as CC_SRC.

Decoding-wise, SHLD/SHRD by immediate count as a 4 operand
instruction because s->T0 and s->T1 actually occupy three op
slots.  The infrastructure used by opcodes in the 0F 3A table
works fine.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>