tcg-ia64: Define TCG_TARGET_INSN_UNIT_SIZE

Using a 16-byte aligned structure achieves best results, both for code
cleanliness and compiled code size.  However, this means that we can't
use the trick of encoding the slot number into the low 2 bits.

Thankfully, we only ever use slot2, so make that explicit in the names
of the relocation functions, and drop the code for other slots.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-mips: Define TCG_TARGET_INSN_UNIT_SIZE

And use tcg pointer differencing functions as appropriate.

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

And use tcg pointer differencing functions as appropriate.

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

Now that all backends do define TCG_TARGET_INSN_UNIT_SIZE,
remove the fallback definition.

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