xtensa: Fix the regression introduce by r15-959-gbe9b3f4375e7

It is not wrong but also not optimal to specify that sibcalls require
register A0 in RTX generation pass, by misleading DFA into thinking it
is being used in function body.
It would be better to specify it in pro_and_epilogue as with 'return'
insn in order to avoid incorrect removing load that restores A0 in
subsequent passes, but since it is not possible to modify each sibcall
there, as a workaround we will preface it with a 'use' as before.

This patch effectively reverts commit r15-959-gbe9b3f4375e7

gcc/ChangeLog:

	* config/xtensa/xtensa-protos.h (xtensa_expand_call):
	Remove the third argument.
	* config/xtensa/xtensa.cc (xtensa_expand_call):
	Remove the third argument and the code that uses it.
	* config/xtensa/xtensa.md (call, call_value, sibcall, sibcall_value):
	Remove each Boolean constant specified in the third argument of
	xtensa_expand_call.
	(sibcall_epilogue): Add emitting '(use A0_REG)' after calling
	xtensa_expand_epilogue.