s390x/css: realize css_sch_build_schib

s390x/css: realize css_sch_build_schib

The S390 virtual css support already has a mechanism to build a
virtual subchannel information block (schib) and provide virtual
subchannels to the guest. However, to pass-through subchannels to
a guest, we need to introduce a new mechanism to build its schib
according to the real device information. Thus we realize a new css
sch_build_schib function to extract the path_masks, chpids, chpid
type from sysfs. To reuse the existing code, we refactor
css_add_virtual_chpid to css_add_chpid.

Reviewed-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Signed-off-by: Xiao Feng Ren <renxiaof@linux.vnet.ibm.com>
Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Message-Id: <20170517004813.58227-5-bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>