LoongArch: Modify fp_sp_offset and gp_sp_offset's calculation method when frame-...

LoongArch: Modify fp_sp_offset and gp_sp_offset's calculation method when frame->mask or frame->fmask is zero.

Under the LA architecture, when the stack is dropped too far, the process
of dropping the stack is divided into two steps.
step1: After dropping the stack, save callee saved registers on the stack.
step2: The rest of it.

The stack drop operation is optimized when frame->total_size minus
frame->sp_fp_offset is an integer multiple of 4096, can reduce the number
of instructions required to drop the stack. However, this optimization is
not effective because of the original calculation method

The following case:
	int main()
	{
  	  char buf[1024 * 12];
  	  printf ("%p\n", buf);
  	  return 0;
	}

As you can see from the generated assembler, the old GCC has two more
instructions than the new GCC, lines 14 and line 24.

	   new                                        old
 10 main:                       | 11 main:
 11   addi.d  $r3,$r3,-16       | 12   lu12i.w $r13,-12288>>12
 12   lu12i.w $r13,-12288>>12   | 13   addi.d  $r3,$r3,-2032
 13   lu12i.w $r5,-12288>>12    | 14   ori $r13,$r13,2016
 14   lu12i.w $r12,12288>>12    | 15   lu12i.w $r5,-12288>>12
 15   st.d  $r1,$r3,8           | 16   lu12i.w $r12,12288>>12
 16   add.d $r12,$r12,$r5       | 17   st.d  $r1,$r3,2024
 17   add.d $r3,$r3,$r13        | 18   add.d $r12,$r12,$r5
 18   add.d $r5,$r12,$r3        | 19   add.d $r3,$r3,$r13
 19   la.local  $r4,.LC0        | 20   add.d $r5,$r12,$r3
 20   bl  %plt(printf)          | 21   la.local  $r4,.LC0
 21   lu12i.w $r13,12288>>12    | 22   bl  %plt(printf)
 22   add.d $r3,$r3,$r13        | 23   lu12i.w $r13,8192>>12
 23   ld.d  $r1,$r3,8           | 24   ori $r13,$r13,2080
 24   or  $r4,$r0,$r0           | 25   add.d $r3,$r3,$r13
 25   addi.d  $r3,$r3,16        | 26   ld.d  $r1,$r3,2024
 26   jr  $r1                   | 27   or  $r4,$r0,$r0
			        | 28   addi.d  $r3,$r3,2032
 				| 29   jr  $r1
gcc/ChangeLog:

	* config/loongarch/loongarch.cc (loongarch_compute_frame_info):
	Modify fp_sp_offset and gp_sp_offset's calculation method,
	when frame->mask or frame->fmask is zero, don't minus UNITS_PER_WORD
	or UNITS_PER_FP_REG.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/prolog-opt.c: New test.

(cherry picked from commit aa8fd7f65683ef9c3b6d2e9306bea2f28b5cadf7)