UPSTREAM: nds32: Fix vDSO clock_getres()

clock_getres in the vDSO library has to preserve the same behaviour
of posix_get_hrtimer_res().

In particular, posix_get_hrtimer_res() does:
    sec = 0;
    ns = hrtimer_resolution;
and hrtimer_resolution depends on the enablement of the high
resolution timers that can happen either at compile or at run time.

Fix the nds32 vdso implementation of clock_getres keeping a copy of
hrtimer_resolution in vdso data and using that directly.

Cc: Greentime Hu <green.hu@gmail.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>
(cherry picked from commit af9abd65983cf3602c03ef3d16fe549ba1f3eeed)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: Ic66e6358c4f5f32abc968a6ebb4868eaa7d07a37