memory: Add support for Exynos SROM driver

This patch adds Exynos SROM controller driver which will handle
save restore of SROM registers during S2R.

Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
[p.fedin@samsung.com: tested on SMDK5410]
Tested-by: Pavel Fedin <p.fedin@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>
[k.kozlowski: Minor COMPILE_TEST adjustments in Kconfig entries]
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>