Transceiver52M: fix viterbi-eq soft bits on platforms where char is unsigned
The viterbi-eq demodulator stores soft bits into chars. "char" is signed on x86/amd64 but unsigned on arm64. On arm64 the stored byte 0x81 (== -127) is read back as +129, so after the sign flip and vectorSlicer() clamp every soft bit collapses to 0.0.
The same issue also appears to be present in the MS code path, so it was (blindly) fixed there as well. The MS fixes are untested!
trx-usrp1: make single daughterboard VTY configurable
Adds the usrp1-singledb enable/disable option to specify the daughterboard configuration on USRP1 devices. This will allow users to use single-daughterboard devices without compliling from source to use the --with-singledb configure option. Also removed some daughterboard configuration related code that wasn't being used. More info in the modified trx-backends.adoc
