sysutils/rovclock: fix build on aarch64, armv6, armv7, mips, mips64, powerpc64

Probably other architectures are also fixed but only those are marked broken.

machine/pio.h is necessary for outl().

PR: 248170
Approved by: portmgr (blanket: build fix (multiple archs))
MFH: 2020Q3 (blanket: build fix (multiple archs))