ARM: at91: suspend both memory controllers on at91sam9263

For the past three years, we have had a #warning in
mach-at91 about the sdram_selfrefresh_enable or
at91sam9_standby functions possibly not working on
at91sam9263. In the meantime a function was added
to do the right thing on at91sam9g45, which looks like
it should also work on '9263.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[nicolas.ferre@atmel.com: remove paragraph in commit message]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>