UPSTREAM: mips: Add clock_gettime64 entry point

With the release of Linux 5.1 has been added a new syscall,
clock_gettime64, that provided a 64 bit time value for a specified
clock_ID to make the kernel Y2038 safe on 32 bit architectures.

Update the mips32 specific vDSO library accordingly with what it has
been done for the kernel syscall exposing the clock_gettime64 entry
point.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
(cherry picked from commit 1f66c45db3302386ca3bb3b5ed05248434237fc9)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: Iddc198f2c93163bb28413ac06d3ac0c50331d0cc