build: include ptrace.h after regs.h

Restore the order of including <sys/reg.h> and <linux/ptrace.h>
headers that was inadvertently changed by commit v4.9-280-g5503dd2.

This should fix build on platforms like m68k where some constants
are defined simultaneously as enums by <sys/reg.h> and as macros
by <asm/ptrace.h>.

* process.c: Include "ptrace.h" after "regs.h".
* signal.c: Likewise.
* syscall.c: Likewise.
* util.c: Likewise.
diff --git a/process.c b/process.c
index a9b76c3..690ca8e 100644
--- a/process.c
+++ b/process.c
@@ -42,12 +42,11 @@
 
 #include "xlat/nt_descriptor_types.h"
 
+#include "regs.h"
 #include "ptrace.h"
 #include "xlat/ptrace_cmds.h"
 #include "xlat/ptrace_setoptions_flags.h"
 
-#include "regs.h"
-
 #define uoff(member)	offsetof(struct user, member)
 #define XLAT_UOFF(member)	{ uoff(member), "offsetof(struct user, " #member ")" }