xtensa: Define HONOR_REG_ALLOC_ORDER as 1

xtensa: Define HONOR_REG_ALLOC_ORDER as 1

Since the commit of the preceding patch for IRA, "ira: Scale save/restore
costs of callee save registers with block frequency" (3b9b8d6cfdf59337f4b7ce10ce92a98044b2657b),
the Xtensa ISA has shown a tendency to allocate slightly more function stack
frames, especially when using the CALL0 ABI.

     /* example */
     extern void foo(void);
     int test(int a) {
       int array[252];
       foo();
       asm volatile (""::"m"(array));
       return a;
     }

     ;; before (-O2 -mabi=call0)
     test:
     	addi	sp, sp, -16
     	s32i.n	a0, sp, 12
     	addmi	sp, sp, -0x400
     	s32i	a2, sp, 1008
     	call0	foo
     	l32i	a2, sp, 1008
     	addmi	sp, sp, 0x400
     	l32i.n	a0, sp, 12
     	addi	sp, sp, 16
     	ret.n

This patch disables the incorrect register save cost estimation in function
prologues/epilogues by defining the HONOR_REG_ALLOC_ORDER macro as 1.

     ;; after (-O2 -mabi=call0)
     test:
     	addmi	sp, sp, -0x400
     	s32i	a0, sp, 1020
     	s32i	a2, sp, 1016
     	call0	foo
     	l32i	a2, sp, 1016
     	l32i	a0, sp, 1020
     	addmi	sp, sp, 0x400
     	ret.n

gcc/ChangeLog:

	* config/xtensa/xtensa.h (HONOR_REG_ALLOC_ORDER):
	New macro definition.

gcc/testsuite/ChangeLog:

	* gcc.target/xtensa/elim_callee_saved.c:
	Revise the test item for the number of mov instructions in the
	assembler output.