Exynos5420: Introduce support for the Peach-Pit board

Exynos5420: Introduce support for the Peach-Pit board

While the Exynos5420 chip is used in both Smdk5420 and in the Peach-Pit
line of devices, there could be other boards using the same chip, so a
common configuration file is being added (exynos5420.h) as well
as two common device tree files (exynos54xx.dtsi & exynos5420.dtsi).

The peach board as declared in boards.cfg is a copy of smdk5420
declaration. The configuration files are similar, but define different
default device trees, console serial ports and prompts.

The device tree files for smdk5420 and peach-pit inherit from the same
common file.

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>