sched/topology: Move the declaration of 'schedutil_gov' to kernel/sched/sched.h

Move it out of the .c file into the shared scheduler-internal header file,
to gain type-checking.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20231009060037.170765-3-sshegde@linux.vnet.ibm.com