regulator: of: setup initial suspend state

Setup initial suspend state to mem, if suspend state is defined for
mem state. This makes sure that the regulators are in proper mode
already from boot.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>