compat: Re-add missing asm/compat.h include to fix compile breakage on s390

For kernels <= 3.0 the backport of 048cd4e5
"compat: fix compile breakage on s390" will break compilation...

Re-add a single #include <asm/compat.h> in order to fix this.

This patch is _not_ necessary for upstream, only for stable kernels
which include the "build fix" mentioned above.
Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/kernel/setup.c

@@ -56,6 +56,7 @@
 #include <asm/ptrace.h>
 #include <asm/sections.h>
 #include <asm/ebcdic.h>
+#include <asm/compat.h>
 #include <asm/kvm_virtio.h>
 
 long psw_kernel_bits	= (PSW_BASE_BITS | PSW_MASK_DAT | PSW_ASC_PRIMARY |