Overclock in UBOOT. Be careful, this is only 'theoretical'
In UBOOT find the /boards/davinci.c file. In there there is a routine called misi_init_r.
There you can add code to change the value pf the PLL1_PLLM register.
Same as above, however you can set the values for PLL2_PLLM and PLL2_DIV2.