ddr: imx: Add 3600 MTps rate support

Add PLL settings for DDR 3600 MTps . This is very similar to 3200 MTps
PLL setting, except the divider is not 9 but 8 .

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>