[RS6000] Merge rs6000_reg_live_or_pic_offset_p into save_reg_p

[RS6000] Merge rs6000_reg_live_or_pic_offset_p into save_reg_p

rs6000_reg_live_or_pic_offset_p is just save_reg_p with special
handling for the pic register and eh_return.  This merge also
simplifies the eh_return handling.  The intent of
https://gcc.gnu.org/ml/gcc-patches/2010-09/msg01838.html was to say
the PIC reg needed to be saved for eh_return, not all gprs.  Of
course, it doesn't hurt to say all gprs need to be saved for eh_return
as that is what the target-independent code does by setting DF live,
but it's unnecessary in the backend.

	* config/rs6000/rs6000.c (rs6000_reg_live_or_pic_offset_p): Merge..
	(save_reg_p): ..into this.  Update all callers.
	(first_reg_to_save): Simplify.

From-SVN: r251115