libbladeRF: Fixed potentially uninitialized status variable

Updated parameter types to a more appropriate unsigned type, and
defaulted status to "success" if 0 length is provided.

This is intended to address build issues (reported on OSX 10.6.8) caused
by status being potentially uninitialized and the associated warnings
being used to generate errors.
libbladeRF: Removing extra loopback function.

Removing the firmware loopback function in preference of adding an
enumerated type to the loopbacks.

NOTE: Currently the firmware loopback does not check for an appropriate
version before trying to set it.  Caution should be used while using
this function for now.
libbladeRF: Remove hardcoded length and use function parameter
libbladeRF: Fixed incorrect buffer resubmission on SW RX overrun (sync i/f)

The handling of RX overruns in the sync interface was logically flawed;
attempting to resubmit a transfer without invalidating the remaining
in-flight transfers would cause transfers to become out of order.

When a SW RX overrun is detected, all transfers are now resubmitted to
maintain proper ordering.
libbladeRF: Warning cleanup - fixes broken Windows build
libbladeRF: Fixed dereferences before NULL checks

Resolves CIDs 1195477 and 1195478
libbladeRF: Removed dead code (addresses CID 1195476)
libbladeRF: [WIP] Renamed and moved backend function table items
libbladeRF: [WIP] Started copying over USB fns
Added a few more usb fns
libbladeRF: [WIP] Working through compilation errors
[WIP] Additional build fixes
libbladeRF: [WIP] Fixed structure renaming build breaker
libbladeRF: [WIP] Reorganized backend-related code, moved to backend/
libbladeRF: [WIP] Stubbed out new libusb backend
libbladeRF: [WIP] Added a few libusb backend functions