arm64: dts: Remove inconsistent use of 'arm,armv8' compatible string

The 'arm,armv8' compatible string is only for software models. It adds
little value otherwise and is inconsistently used as a fallback on some
platforms. Remove it from those platforms.

This fixes warnings generated by the DT schema.

Reported-by: Michal Simek <michal.simek@xilinx.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Antoine Tenart <antoine.tenart@bootlin.com>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Chanho Min <chanho.min@lge.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Wei Xu <xuwei5@hisilicon.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Acked-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Chunyan Zhang <zhang.lyra@gmail.com>
Acked-by: Robert Richter <rrichter@cavium.com>
Acked-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>