arm64: big-endian: add big-endian support to top-level arch Makefile

This patch adds big-endian support to the AArch64 top-level Makefile.
This currently just passes the relevant flags to the toolchain and is
predicated on a Kconfig option that will be introduced later on.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: a0974e6e217aead196033d72f898e2acb575304d
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>