Most servos run fine on 5V, with only slight torque drop.
You could try running the +5V and Gnd from the Easy Driver board to the Arduino +5V and GND for powering the Arduino. However, I don't know how much current that 5V will manage to provide.
In fact, I'm not sure 1.5A is enough for one stepper and two servos. Bigger servos, when stalled, easily draw 1 amp each. Add 0.3-0.6 amps for the stepper, and you should be using a 3A supply.
What I would do is build a 6V/3A supply for the servos using an adjustable LM350 regulator, two resistors, and two capacitors. Feed it 12V, and feed its output to the servo power. Feed the Arduino only from the 5V on the Easy Driver board. I'd also use a 12V/3A power supply for that setup.http://www.ti.com/lit/ds/snvs772a/snvs772a.pdf