HomeFreeBSD

Rename mkdumpheader() and group EKCD functions in kern_shutdown.c.

Description

Rename mkdumpheader() and group EKCD functions in kern_shutdown.c.

This helps simplify the code in kern_shutdown.c and reduces the number
of globally visible functions.

No functional change intended.

Reviewed by: cem, def
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D11603