tcg/sparc64: Disable direct linking for goto_tb

Something is wrong with this code, and also wrong with gdb on the
sparc systems to which I have access, so I cannot debug it either.
Disable for now, so the release is not broken.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>