arm64: dts: hikey: Add pstore support for HiKey

This patch reserves some memory in the DTS and sets up a
pstore device tree node to enable pstore support on HiKey.

Cc: Kees Cook <keescook@chromium.org>
Cc: Guodong Xu <guodong.xu@linaro.org>
Cc: Haojian Zhuang <haojian.zhuang@linaro.org>
Cc: Wei Xu <xuwei5@hisilicon.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: devicetree@vger.kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>