sunxi: Convert sun7i boards to use auto dram configuration

Currently we've separate detailed dram settings for all sun7i boards, this
moves them over to using auto dram configuration so that we can get rid of
all the per board dram_foo.c files.

This has been tested on a A20-Olinuxino-Lime, A20-Olinuxino_MICRO, Bananapi,
Bananapro, Cubieboard2, Cubietruck, Mele_M3 and a Linksprite_pcDuino3.

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