A long long time ago the register keyword told the compiler to store
the corresponding variable in a CPU register, but it is not relevant
for any compiler used in the FreeBSD world today.
ANSIfy related prototypes while here.
Reviewed by: cem, jhb
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D10193
No functional change, only trivial cases are done in this sweep,
Drivers that can get further enhancements will be done independently.
Discussed in: freebsd-current