Configure ubx ITFM on supporting versions

[aubin-cldn]

The UBX configuration CFG-ITFM-ENABLE has been removed for u-blox FW versions greater than 1.32 (so 1.40, 1.50...). Thus, trying to configure this parameter results in a NAK response, and prevents PX4 from configuring the receiver.

This MR:

• Saves the FW version of the receiver in the variable _firmware_version;
• Enables the configuration of CFG-ITFM-ENABLE on _firmware_version < 1.40.

To convert the FW version from a string to a float, uses atof on the last part of the string (after the space delimiting the number in the string), allowing to differentiate values like HPG 1.51 and HPGL1L5 1.40 for example.