ARM: SAMSUNG: Add watchdog reset driver

This patch adds a watchdog reset driver that can be used on Samsung SoCs
that do not provide dedicated reset method. It replaces the legacy
helper function that relies on static IO mapping.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Tested-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>