s390/sclp_early: Pass sccb pointer to every *_detect() function

Add a sccb pointer parameter to *_detect() functions instead of accessing
the global sccb_early variable directly.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>