csu: add crtbrand.o dependency on sys/param.h

FreeBSD_version is recorded in *crt1.o and crti.o via crtbrand.o. Add
an explicit dependency to pick up FreeBSD_version bumps.

Additional changes are required to fully plumb *crt1.o dependencies
through the build.

Reported by: bapt
Reviewed by: bapt
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D43417