[AArch64] Remove aarch64_frame_pointer_required

[AArch64] Remove aarch64_frame_pointer_required

To implement -fomit-leaf-frame-pointer, there are 2 places where we need
to check whether we have to use a frame chain (since register allocation
may allocate LR in a leaf function that omits the frame pointer, but if
LR is spilled we must emit a frame chain).  To simplify this do not force
frame_pointer_needed via aarch64_frame_pointer_required, but enable the
frame chain in aarch64_layout_frame.  Now aarch64_frame_pointer_required
can be removed and aarch64_can_eliminate is simplified.

    gcc/
	* config/aarch64/aarch64.c (aarch64_frame_pointer_required)
	Remove.
	(aarch64_layout_frame): Initialise emit_frame_chain.
	(aarch64_can_eliminate): Remove omit leaf frame pointer code.
	(TARGET_FRAME_POINTER_REQUIRED): Remove define.

    testsuite/
	* gcc.target/aarch64/dwarf-cfa-reg.c: Update.

From-SVN: r254533