[S390] hvc_iucv: Refactor console and device initialization

The console_initcall() order might pick up the hvc_iucv device as preferred
console even if it is not yet initialized.
Move HVC console instantiation to hvc_iucv_init() and cleanup device driver
initialization.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>