hppa/vdso: Add wrappers for vDSO functions

The upcoming parisc (hppa) v6.11 Linux kernel will include vDSO
support for gettimeofday(), clock_gettime() and clock_gettime64()
syscalls for 32- and 64-bit userspace.
The patch below adds the necessary glue code for glibc.

Signed-off-by: Helge Deller <deller@gmx.de>

Changes in v2:
- add vsyscalls for 64-bit too