s390/facilities: add helper tool to generate facility lists
Modifying the architecture level set facility lists was always very
error prone. Given the numbering of the facility bits within the
Principles of Operation, where the most significant bit number is 0,
it happened a lot of times that wrong bits were set or cleared.
Therefore this patch adds a tool "gen_facilities" which generates
include/generated/facilites.h. The definition of the bits to be set
is contained within arch/s390/include/asm/facilities_src.h and can be
easily extended to e.g. also generate such lists for the KVM module.