s390: report new CPU capabilities

Add hardware capability bits and features tags to /proc/cpuinfo
for 4 new CPU features:
  "Vector-Enhancements Facility 2" (tag "vxe2", hwcap 2^15)
  "Vector-Packed-Decimal-Enhancement Facility" (tag "vxp", hwcap 2^16)
  "Enhanced-Sort Facility" (tag "sort", hwcap 2^17)
  "Deflate-Conversion Facility" (tag "dflt", hwcap 2^18)

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>