print: add nouserprint argument

For some usecases, silencing syscall_print()s is ideal. A good example
of that is syzkaller, which uses logs to detect crashes and a badly
timed syscall_print() could interfere.

Add a nouserprint argument which skips printing on syscall_print().

kernel-src/sys/syscalls/print.c

@@ -4,12 +4,18 @@
 #include <mutex.h>
 #include <util.h>
 #include <arch/cpu.h>
+#include <kernel/kernel_args.h>
+
+DEFINE_KERNEL_ARGUMENT(nouserprint, bool);
 
 syscallret_t syscall_print(context_t *context, char *message) {
 	syscallret_t ret = {
 		.ret = -1
 	};
 
+	if (GET_KERNEL_ARGUMENT(nouserprint, bool))
+		goto leave;
+
 	static MUTEX_DEFINE(mutex);
 
 	size_t len;
@@ -35,6 +41,7 @@ syscallret_t syscall_print(context_t *context, char *message) {
 	arch_e9_putc('\n');
 	MUTEX_RELEASE(&mutex);
 
+leave:
 	ret.errno = 0;
 	ret.ret = 0;
 	return ret;