target/cris: Plug leakage of TCG temporaries

Add and fix deallocation of temporary TCG registers in CRIS code
generation.

Tested-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Change-Id: I17fce5d95bdc4418337ba885d53ba97afb1bafcc
Signed-off-by: Stefan Sandström <stefans@axis.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210219124416.28178-1-stefans@axis.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>