Simplify frame layout for stack probing

Simplify frame layout for stack probing

This patch makes some changes to the frame layout in order to simplify
stack probing.  We want to use the save of LR as a probe in any non-leaf
function.  With shrinkwrapping we may only save LR before a call, so it
is useful to define a fixed location in the callee-saves. So force LR at
the bottom of the callee-saves even with -fomit-frame-pointer.

Also remove a rarely used frame layout that saves the callee-saves first
with -fomit-frame-pointer.  Doing so allows the store of LR to be used as
a valid stack probe in all frames.

    gcc/
	* config/aarch64/aarch64.c (aarch64_layout_frame):
        Ensure LR is always stored at the bottom of the callee-saves.
        Remove rarely used frame layout which saves callee-saves at top of
        frame, so the store of LR can be used as a valid probe in all cases.

From-SVN: r254112