sun6i: Add dram initialization code

Add full support for dram initialization, using a fixed clock and autodetection
of the memory organization (numbers of channels, bus-width, etc.).

This is based on dram_sun6i.c and dram.h from u-boot in the Allwinner A31 SDK,
extended with extra initialization sequences and the autodetect algorithm
from boot0.

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