sun6i: Drop some "unknown magic" from dram init

Allwinner tells us that this bit of code is the rtc ram being used to detect
coming out of "super-standby" mode, and if that is the case, going out of
self-refresh mode.

Since we do not support "super-standby" mode, this can be dropped.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>