s390/pgalloc: add virt/phys address handling to base asce functions

The base asce functions create/free page tables open-coded to make
sure that the returned asce and page tables do not make use of any
enhanced DAT features like e.g. large pages. This is required for some
I/O functions that use an asce, like e.g. some service call requests.

Handling of virtual vs physical addresses is missing; therefore add
that now.

Note: this currently doesn't fix a real bug, since virtual addresses
are indentical to physical ones.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>