FMCOMMS2 Source/Sink: Use enums for booleans

This permits to use a drop-down menu with the "True" and "False" options
(instead of having to type that in a text field).

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
FMCOMMS2 Source: Enhance block with new parameters

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
FMCOMMS2 Sink: Enhance block with new parameters

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>