[LRA]: Fix sparc bootstrap after recent patch for fp elimination for avr LRA port

[LRA]: Fix sparc bootstrap after recent patch for fp elimination for avr LRA port

The recent patch for fp elimination for avr LRA port modified an assert
which can be wrong for targets using hard frame pointer different from
frame pointer.  Also for such ports spilling pseudos assigned to fp
was wrong too in the new code.  Although this code is not used for any target
currently using LRA except for avr.  Given patch fixes the issues.

gcc/ChangeLog:

	* lra-eliminations.cc (update_reg_eliminate): Fix the assert.
	(lra_update_fp2sp_elimination): Use HARD_FRAME_POINTER_REGNUM
	instead of FRAME_POINTER_REGNUM to spill pseudos.