Add fx2lafw firmware for FX2 devices with sigrok VID/PID.

Add fx2lafw firmware for FX2 devices with sigrok VID/PID.

The two new firmware images fx2lafw-sigrok-fx2-{8,16}ch.fw can be used
on Cypress FX2 devices where one of the two official sigrok fx2lafw
USB VID/PID pairs is hardcoded in an external EEPROM.

The sigrok project owns USB product IDs allocated via the Openmoko project:

  http://wiki.openmoko.org/wiki/USB_Product_IDs

The following two VID/PID pairs are available for devices that use
a Cypress FX2(LP) chip *directly* as 8-channel or 16-channel logic analyzer,
and use the respective USB-based protocol. They are *not* meant for
other devices which just happen to also have an FX2 (e.g. in addition to
an FPGA) and/or devices that use a different USB-based protocol.

 - 1D50:608C: fx2lafw-sigrok-fx2-8ch.fw

 - 1D50:608D: fx2lafw-sigrok-fx2-16ch.fw