dts:exynos:update pinctrl size-cells and fix child regs

This change is required to avoid warnings about invalid
size-cells defined in device-tree pinctrl nodes for Exynos.

Tested on:
- Odroid U3
- Odroid XU3

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Tested-by: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Minkyu Kang <mk7.kang@samsung.com>