KVM: s390: Features for 4.19

- initial version for host large page support. Must be enabled with
  module parameter hpage=1 and will conflict with the nested=1
  parameter.
- enable etoken facility for guests
- Fixes
Merge tag 'hlp_stage1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into kvms390/next

KVM: s390: initial host large page support

- must be enabled via module parameter hpage=1
- cannot be used together with nested
- does support migration
- does support hugetlbfs
- no THP yet