sunxi: H6: move LPDDR3 timing definition into separate file

Currently the H6 DRAM driver only supports one kind of LPDDR3 DRAM.
Split the timing parameters for this LPDDR3 configuration  into a
separate file, to allow selecting an alternative later at compile time
(as the sunxi-dw driver does).

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>