What LCD display are you using? Are you seeing overall flickering, periodic streaks across the display, color problems, or borders not right?
For the crossbar priority setting refer to chapter 12 of the reference manual. The following example will set the LCD controller to highest priority.
#define MCF_XBS_PRS1 (*(volatile unsigned int*)0xfc004100)
MCF_XBS_PRS1 = 0x65400213;
However, this is a trade off. You may have performance problems with networking or other issues.