tc_fill_vdso_timehands32(): fix

On 64bit, there is a 4-byte hole in struct vdso_timekeep32 after
tk_current, if the structure is not packed. This is due to the MD
th_x86_pvc_last_systime being 64bit.

Change amd64 VDSO_TIMEHANDS_MD32 to not use uint64_t, replace it with
pair of uint32_t, as it is done for all other members.

PR: 273085
Sponsored by: The FreeBSD Foundation
MFC after: 1 week