re PR target/26504 (compute_frame_pointer_to_cfa_displacement error for avr target with --with-dwarf2)

	* config/avr/predicates.md: New file.
	* config/avr/avr.md: Include it.
	(REG_SP): New constant.
	(peepholes): Use predicates.
	(sbrx_branch, sbrx_and_branchhi, sbrx_and_branchsi, branch, rvbranch,
	difficult_branch,  difficult_rvbranch, cbi, sbi, sbix_branch,
	sbix_branch_bit7, sbix_branch_tmp, sbix_branch_tmp_bit7): Ditto.
	PR target/26504
	* config/avr/avr.h (FRAME_POINTER_CFA_OFFSET): Define.

From-SVN: r117616