The Pi model B revisions 1 and 2 only exposes one gpio with hardware PWM support (gpio 18 on pin 12 of the expansion header).
The Pi models A+ and B+ expose gpios 12, 13, 18, and 19 with hardware PWM support. There are only two PWM channels though so you still only have two hardware PWM settings to choose from rather than 4.
However PWM suitable for driving motors may be generated by software on all gpios using either software or hardware timing of the pulses.
So the answer to your question is yes, you can control two motors (with PWM to allow speed control) using the Pi and a L293D.