s390/mm: Get rid of fault type switch statements

s390/mm: Get rid of fault type switch statements

With GMAP_FAULT fault type gone, there are only KERNEL_FAULT and
USER_FAULT fault types left. Therefore there is no need for any fault
type switch statements left.

Rename get_fault_type() into is_kernel_fault() and let it return a
boolean value. Change all switch statements to if statements. This
removes quite a bit of code.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/r/20241022120601.167009-11-imbrenda@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>