ARM: at91: define LPDDR types

The Atmel MPDDR controller support LPDDR2 and LPDDR3 memories, add their
types.

Cc: <stable@vger.kernel.org> # 4.4+
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>