Add support for next Raspberry OS 64 bits

[pleira]

Add support in cmake/Modules/FindRTLSDR.cmake for next Raspberry OS 64 bits by looking for librtlsrd0 in /usr/lib/aarch64-linux-gnu.

[Baldomo]

Hi, I opened a PR for this. I hope we can get a response from the devs, but you can pull my PR if you need the fix ASAP.