S/390: Get cache information via sysconf

This patch adds support to query cache information on s390
via sysconf() function - e.g. with _SC_LEVEL1_ICACHE_SIZE.
The attributes size, linesize and assoc can be queried
for cache level 1 - 4 via "extract cpu attribute" instruction,
which was first available with z10.

* NEWS: Mention sysconf() cache information support for s390.
* sysdeps/unix/sysv/linux/s390/sysconf.c: New File.