arc: Update stack size computation when accumulator registers are available.

arc: Update stack size computation when accumulator registers are available.

When accumulator registers are available in a processor, they need to
be save onto stack durring interrupts.  We were already doing so, but
the stack size was wrongly computed in the case other than ARC600.

gcc/

	* config/arc/arc.c (arc_compute_frame_size): Remove condition when
	computin checking accumulator regs.
	(arc_expand_prologue): Update comments.
	(arc_expand_epilogue): Likewise.

Signed-off-by: Claudiu Zissulescu <claziss@synopsys.com>