tcg/sparc: Add tcg_out_jmpl_const for better tail calls

tcg/sparc: Add tcg_out_jmpl_const for better tail calls

Due to mapping changes, we now rarely place the code_gen_buffer
near the main executable.  Which means that direct calls will
now rarely be in range.

So, always use indirect calls for tail calls, which allows us to
avoid clobbering %o7, and therefore we need not save and restore it.

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