tcg: Introduce temp_load

Unify all of the places that realize a temporary into a register.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg: Tidy temporary allocation

In particular, make sure the memory is memset before use.
Continues the increased use of TCGTemp pointers instead of
integer indices where appropriate.

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

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg: Implement indirect memory registers

That is, global_mem registers whose base is another global_mem
register, rather than a fixed register.

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-sparc: Tidy global register initialization

Create tables for the various global registers that need allocation.
Remove one level of indirection from  gregnames and fregnames.

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-sparc: Use global registers for the register window

Via indirection off cpu_regwptr.

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