program loading: unify on struct prog

Instead of having different structures for loading
ramstage and payload align to using struct prog.
This also removes arch_payload_run() in favor of
the prog_run() interface.

Change-Id: I31483096094eacc713a7433811cd69cc5621c43e
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/8849
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>

src/arch/arm/boot.c

@@ -29,8 +29,3 @@ void arch_prog_run(struct prog *prog)
 	doit = prog_entry(prog);
 	doit(prog_entry_arg(prog));
 }
-
-void arch_payload_run(struct payload *payload)
-{
-	arch_prog_run(&payload->prog);
-}