I found below comment from i.MX25 RM, Chapter 44. Touch Screen Controller (TSC) and Analog-to-Digital Converter (ADC).
Supports general-purpose analog measurements (such as temperature and voltage) with three input channels (aux0, aux1, aux2), or 8 input channels if touch interface is not used.
So I believe ADC channel for TSC can be used for general purpose ADC but is there any body who can confirm it? If there is any limitation to use for this purpose, please let me know.