We're going to want at least some of the NeonGen* typedefs
for the refactored 32-bit Neon decoder, so move them all
to translate.h since it makes more sense to keep them in
one group.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200430181003.21682-23-peter.maydell@linaro.org