ARM: at91: sam9g45: shutdown ddr1 too when rebooting

Like we are doing on DDR0 we need to cleanly shutdown DDR1 if it is
used before rebooting.
If DDR1 is not initialized, we check it and avoid dereferencing its address.
Even by adding two more instructions, we are able to complete the procedure
within a single cache line.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Olof Johansson <olof@lixom.net>