ARM: EXYNOS: reset Little cores when cpu is up

The cpu booting of exynos5422 has been still broken since we discussed
it in last year[1]. This patch is inspired from Odroid XU3
code (Actually, it was from samsung exynos vendor kernel)[2]. This weird
reset code was founded exynos5420 octa cores series SoCs and only
required for the first boot core is the Little core (Cortex A7).
Some of the exynos5420 boards and all of the exynos5422 boards will require
this code.

There is two ways to check the little core is the first cpu. One is
checking GPG2CON[1] GPIO value and the other is checking the cluster
number of the first cpu. I selected the latter because it's more easier
than the former.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-June/350632.html
[2] https://patchwork.kernel.org/patch/6782891/



Cc: Kevin Hilman <khilman@kernel.org>
Cc: Javier Martinez Canillas <javier@osg.samsung.com>
Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Chanho Park <parkch98@gmail.com>
Cc: <stable@vger.kernel.org> # 4.1+
[k.kozlowski: Adding stable for v4.1+, reformat comment]
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>