target/i386: adjust decoding of J operand

target/i386: adjust decoding of J operand

gen_jcc() has been changed to accept a relative offset since the
new decoder was written.  Adjust the J operand, which is meant
to be used with jump instructions such as gen_jcc(), to not
include the program counter and to not truncate the result, as
both operations are now performed by common code.

The result is that J is now the same as the I operand.

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