Return the device actual supported sample rate in the SoapySDR module

[skgsergio]

Currently, this SoapySDR module returns some fixed values as the sample rate range and only those two values as the list of sample rates.

This causes some issues with apps using SoapySDR to work with LimeSDR devices:

• Those using the range allow setting the sample rate to values over LimeSDR Mini specification and cause issues.
• Those using the list of sample rates only get 0.1 and 65 Msps values as is what the module says and for example in LimeSDR Mini 65 Msps is way higher than the 30.72 Msps specification. Also, you don't get more values you can use.

This PR attempts to fix this by getting device values calling to LMS_GetSampleRateRange and returning those in the case of the range function or creating some stepped values in between the min and max values.

In any case, if the LMS_GetSampleRateRange fails it falls back to the previous hardcoded values.

[skgsergio]

Thank you for merging this! 🚀