tcg: Add tcg-be-null.h

This is a no-op backend data implementation, for those targets that
are not currently using the load/store optimization path.

This is prepatory to always requiring these functions in all backends.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg: Add tcg-be-ldst.h

Move TCGLabelQemuLdst and related stuff out of tcg.h.

Signed-off-by: Richard Henderson <rth@twiddle.net>
configure: Remove CONFIG_QEMU_LDST_OPTIMIZATION

No longer used.

Signed-off-by: Richard Henderson <rth@twiddle.net>