S390: Add new s390 platform.

The new IBM z13 is added to platform string array.
The macro _DL_PLATFORMS_COUNT is incremented to 8,
because it was not incremented by commit
"S/390: Sync AUXV capabilities and archs with kernel".

ChangeLog:

	* sysdeps/s390/dl-procinfo.c (_dl_s390_cap_flags): Add z13.
	* sysdeps/s390/dl-procinfo.h (_DL_PLATFORMS_COUNT): Increased.

(cherry picked from commit a1b0488f)