drivers/tty: make pty.c slightly more explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/tty/Kconfig:config LEGACY_PTYS
drivers/tty/Kconfig:    bool "Legacy (BSD) PTY support"

...and:

drivers/tty/Kconfig:config UNIX98_PTYS
drivers/tty/Kconfig:    bool "Unix98 PTY support" if EXPERT

combined with this:

obj-$(CONFIG_LEGACY_PTYS)       += pty.o
obj-$(CONFIG_UNIX98_PTYS)       += pty.o

...meaning that it currently is not being built as a module by anyone.

Lets remove the traces of modularity we can so that when reading the
driver there is less doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.

We don't delete the module.h include since other parts of the file are
using content from there.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -7,7 +7,6 @@
  */
 
 #include <linux/module.h>
-
 #include <linux/errno.h>
 #include <linux/interrupt.h>
 #include <linux/tty.h>
@@ -501,6 +500,10 @@ static int pty_bsd_ioctl(struct tty_struct *tty,
 }
 
 static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
+/*
+ * not really modular, but the easiest way to keep compat with existing
+ * bootargs behaviour is to continue using module_param here.
+ */
 module_param(legacy_count, int, 0);
 
 /*
@@ -877,4 +880,4 @@ static int __init pty_init(void)
 	unix98_pty_init();
 	return 0;
 }
-module_init(pty_init);
+device_initcall(pty_init);