LinuxKPI: Added jiffies64_to_msecs for amdkfd compatibility

jiffies64_to_msecs is used by kfd_process.c in the amd/amdkfd driver
from Linux kernel 6.12.

Submitted by: Sourojeet Adhikari
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D58075