gcc: xtensa: fix PR target/108876

gcc/
	PR target/108876
	* config/xtensa/xtensa.cc (xtensa_expand_epilogue): Drop emit_use
	for A0_REG.
	* config/xtensa/xtensa.md (sibcall, sibcall_internal)
	(sibcall_value, sibcall_value_internal): Add 'use' expression
	for A0_REG.