WIP: Modify the RXVGA2 calibration routines.
Calibration update.
libbladeRF: Moved LPF DC tuning value write into address loop

This is just for readability. There's no functional change, since
there's only 1 address to loop over anyway.
bladeRF-cli: Workaround - Added retry loop to TXLPF calibration

The TXLPF calibration appears to fail on the first two attempts to
run it. As a temporary workaround, a retry loop has been added
around attempts to run this calibration.
libbladeRF: Stubbed out autocal test program
Use linear interp to get first guess at DC offset values
Integer interpolation and apply rx auto cal parameters
Touched up output
Fixed bad interpolation, type promotion needed.
bladeRF-cli: Removed 'calibrate' cmd implementation

This command will be re-implemented using the autocalibration routines
added in following commits
libbladeRF: [WIP] Began adding RX DC autocal into lib
bladeRF-cli: 'calibrate' command performs RX DC calibration
libbladeRF: Preliminary bladerf_calibrate_dc for RX DC offset
libbladeRF: [WIP] Jotted down TX DC calibration approach
[WIP] Hacked in functionality to check RX DC cal over freq & gains.

This code will not be merged into master. The calibration code may
be moved up to the CLI, and some of the original LMS calibration
routines reverted.