tcg/sparc: Support unaligned access for user-only

This is kinda sorta the opposite of the other tcg hosts, where
we get (normal) alignment checks for free with host SIGBUS and
need to add code to support unaligned accesses.

This inline code expansion is somewhat large, but it takes quite
a few instructions to make a function call to a helper anyway.

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