First: Please run the xf86config program to create a correct configuration.
You can turn off hardware cursor by inserting the following line in the Device section of the XF86Config file:
Or turn off hardware acceleration:
Or turn off MMIO
Please don't specify the amount of video RAM you have or which chipset you have in the config file, let the driver probe for this. Also please don't put any "clocks" line in the device section since these chips have a fully programmable clock that can take (almost) any modeline you throw at it. It might fail at some specific clock values but you should just try a slightly different clock and it should work.