As you probably know, sprpck.exe does not accept png files.
I need it.
I wrote it.
So, you can use it online : http://devlynx.ti-fr.com/sprpck.php
Choose a png file to upload, the mode (full litteral or compact) and then enjoy.
Output provides : palette in C format, sprite in C format and recommended values for SPRCTL0 and SPRCTL1.
Note, it's in "beta" phase, compact mode is not 100% optimal.
If you have any question...