build: alloc space for sched list in the link file

Creates a section to contain scheduler entry pointers that are gathered
together into an array. This will allow, in a follow-on patch, scheduler
entries to be automatically gathered together into the array for
automatic parsing.

Signed-off-by: Jonathan Creekmore <jonathan.creekmore@gmail.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>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/arch/arm/xen.lds.S

@@ -57,6 +57,10 @@ SECTIONS
        . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)
        *(.data)
+       . = ALIGN(8);
+       __start_schedulers_array = .;
+       *(.data.schedulers)
+       __end_schedulers_array = .;
        *(.data.rel)
        *(.data.rel.*)
        CONSTRUCTORS

xen/arch/x86/xen.lds.S

@@ -80,6 +80,10 @@ SECTIONS
        __stop___pre_ex_table = .;
 
        *(.data.read_mostly)
+       . = ALIGN(8);
+       __start_schedulers_array = .;
+       *(.data.schedulers)
+       __end_schedulers_array = .;
        *(.data.rel.ro)
        *(.data.rel.ro.*)
   } :text