arm64: dts: exynos: Correct psci compatible used on Exynos7

arm64: dts: exynos: Correct psci compatible used on Exynos7

It's not possible to reboot or poweroff Exynos7420 using PSCI. Instead
we need to use syscon reboot/poweroff drivers, like it's done for other
Exynos SoCs. This was confirmed by checking vendor source and testing it
on Samsung Galaxy S6 device based on this SoC.

To be able to use custom restart/poweroff handlers instead of PSCI
functions, we need to correct psci compatible. This also requires us to
provide function ids for CPU_ON and CPU_OFF.

Fixes: fb026cb65247 ("arm64: dts: Add reboot node for exynos7")
Fixes: b9024cbc937d ("arm64: dts: Add initial device tree support for exynos7")
Signed-off-by: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Link: https://lore.kernel.org/r/20201107133926.37187-2-pawel.mikolaj.chmiel@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>