arm64: Remove the aux_context structure

This patch removes the aux_context structure (and the containing file)
to allow the placement of the _aarch64_ctx end magic based on the
context stored on the signal stack.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --cc arch/arm64/include/asm/sigcontext.h
Simple merge

diff --cc arch/arm64/kernel/signal.c
Simple merge