The PSoC5LP TRM states explicitely (Chapter 16, page 91):
IMO has a USB mode that synchronizes to USB host traffic, requiring no external crystal for USB. (USB equipped parts
So it can run without crystal.
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AN57473 states http://www.cypress.com/index.cfm?rID=39404
This application note shows you how to do simple data
transfer with PSoC 3 and PSoC 5LP using USB HID. The
PSoC devices include a dedicated Full-speed (FS)
12 Mbps USB 2.0 peripheral, which uses an internal
oscillator – a crystal is not required. The PSoC Creator
IDE and the USBFS Component make it possible to
quickly build an application. A mouse and a joystick are
used as examples.