LinuxKPI: maths64: implement roundup_u64()
Needed by a wifi driver update.
Sponsored by: The FreeBSD Foundation (initially)
Reviewed by: dumbbell
Differential Revision: https://reviews.freebsd.org/D52080
(cherry picked from commit 2a44e10edb13e6b2be7fa2814b418a6959cb1171)
(cherry picked from commit 88122c8eb70d81decb7c6dd16e551c3df6ad3818)