i.MX6SLL has MMDC1 ipg clock in CCM CCGR, add it into
clock tree for clock management.
Signed-off-by: NAnson Huang <Anson.Huang@nxp.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NStephen Boyd <sboyd@kernel.org>