[AArch64] Add support for TARGET_COMPUTE_FRAME_LAYOUT

[AArch64] Add support for TARGET_COMPUTE_FRAME_LAYOUT

The patch adds support for the TARGET_COMPUTE_FRAME_LAYOUT hook on AArch64
and removes unneeded frame layout recalculation.

2018-09-13  Vlad Lazar  <vlad.lazar@arm.com>

	* config/aarch64/aarch64.h (TARGET_COMPUTE_FRAME_LAYOUT): Define.
	* config/aarch64/aarch64.c (aarch64_expand_prologue): Remove
	aarch64_layout_frame call.
	(aarch64_expand_epilogue): Likewise.
	(aarch64_initial_elimination_offset): Likewise.
	(aarch64_get_separate_components): Likewise.
	(aarch64_use_return_insn_p): Likewise.
	(aarch64_layout_frame): Remove unneeded check.

From-SVN: r264263