ARM64:VDSO: Improve __do_get_tspec, don't use udiv

ARM64:VDSO: Improve __do_get_tspec, don't use udiv

In most other targets (x86/tile for an example),
the division in __do_get_tspec is converted into
a simple loop.  The main reason for this is
because the result of this division is going
to be either 0 or 1.
This changes the division to the simple loop
and thus speeding up gettimeofday.

Signed-off-by: Andrew Pinski <apinski@cavium.com>
Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com>