sunxi: H6: DRAM: follow recommended PHY init algorithm

sunxi: H6: DRAM: follow recommended PHY init algorithm

The DRAM controller manual suggests to first program the PHY
initialisation parameters to the PHY_PIR register, and then set bit 0 to
trigger the initialisation. This is also used in boot0.

Follow this recommendation by setting bit 0 in a separate step.

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>