sched: register the schedulers into the list

sched: register the schedulers into the list

Adds a simple macro to place a pointer to a scheduler into an array
section at compile time. Also, goes ahead and generates the array
entries with each of the schedulers.

Signed-off-by: Jonathan Creekmore <jonathan.creekmore@gmail.com>
Acked-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>