if Intel Galileo does not work with 100% CPU usage all the time I believe it will be enough
The LM7805 is a very stable voltage controller, you can turn it on own battery that powers the motors, considering the battery has at least 7 volts ...
if you think you will not endure, you can search for a scheme that uses the LM7805 and the 2n2055 that provides you an output voltage of 5 volts and 5A