libbladeRF: Added FPGA and FW version compatibility checks

Error codes and warnings have been added to cases where a firwmare
or FPGA upgrade is required for proper operation.
libbladeRF: Warn about incompatible firmware based upon # altsettings

As firmware v0.4, the bladeRF should present 4 altsettings on
interface 0. If we don't see that, it's an indicator of very old and
incompatible firmware.