certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID

Align with the new macros and add appropriate include files.

Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Link: https://lore.kernel.org/lkml/20201120180426.922572-9-mic@digikod.net
Link: https://lore.kernel.org/lkml/160751620296.1238376.1118832878833351723.stgit@warthog.procyon.org.uk
Link: https://lore.kernel.org/lkml/20210114151909.2344974-6-mic@digikod.net
Link: https://lore.kernel.org/lkml/20210121155513.539519-6-mic@digikod.net