[AArch64] Set ctz rtx_cost (PR93565)

[AArch64] Set ctz rtx_cost (PR93565)

Combine sometimes behaves oddly and duplicates ctz to remove an unnecessary
sign extension.  Avoid this by setting the cost for ctz to be higher than
that of a simple ALU instruction.  Deepsjeng performance improves by ~0.6%.

gcc/
	PR rtl-optimization/93565
	* config/aarch64/aarch64.c (aarch64_rtx_costs): Add CTZ costs.

testsuite/
	PR rtl-optimization/93565
	* gcc.target/aarch64/pr93565.c: New test.