xtensa: drop unneeded platform/hardware.h headers

platform/hardware.h no longer supply any information for processor.h,
vectors.h, setup.c or vmlinux.lds.S, don't include it.
This header is now empty in the platforms/iss, so remove it altogether.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/setup.c

@@ -47,8 +47,6 @@
 #include <asm/smp.h>
 #include <asm/sysmem.h>
 
-#include <platform/hardware.h>
-
 #if defined(CONFIG_VGA_CONSOLE) || defined(CONFIG_DUMMY_CONSOLE)
 struct screen_info screen_info = {
 	.orig_x = 0,