target/i386: Reorder DisasContext members

Sort all of the single-byte members to the same area
of the structure, eliminating 8 bytes of padding.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210514151342.384376-29-richard.henderson@linaro.org>