qemuBuildFloppyCommandLineControllerOptions: Extract formatting of implicit/explicit fdc

qemuBuildFloppyCommandLineControllerOptions: Extract formatting of implicit/explicit fdc

qemuBuildFloppyCommandLineControllerOptions was generating config for
both the implicit and explicit fdc. The explicit FDC is using '-device'
and thus will need to be converted to JSON.

Split up the lookup of the floppy drive configs from the actual command
generation.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>