docs: serial: move it to the driver-api

The contents of this directory is mostly driver-api stuff.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/driver-api/index.rst

···
    pti_intel_mid
    pwm
    rfkill
+   serial/index
    sgi-ioc4
    sm501
    smsc_ece1099

Documentation/serial/driver.rst Documentation/driver-api/serial/driver.rst

···
 	This call must not sleep
 
   set_ldisc(port,termios)
-	Notifier for discipline change. See Documentation/serial/tty.rst.
+	Notifier for discipline change. See Documentation/driver-api/serial/tty.rst.
 
 	Locking: caller holds tty_port->mutex
 

Documentation/serial/index.rst Documentation/driver-api/serial/index.rst

···
-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ==========================
 Support for Serial devices

MAINTAINERS

···
 MOXA SMARTIO/INDUSTIO/INTELLIO SERIAL CARD
 M:	Jiri Slaby <[e-mail]>
 S:	Maintained
-F:	Documentation/serial/moxa-smartio.rst
+F:	Documentation/driver-api/serial/moxa-smartio.rst
 F:	drivers/tty/mxser.*
 
 MR800 AVERMEDIA USB FM RADIO DRIVER
···
 P:	Comtrol Corp.
 W:	http://www.comtrol.com
 S:	Maintained
-F:	Documentation/serial/rocket.rst
+F:	Documentation/driver-api/serial/rocket.rst
 F:	drivers/tty/rocket*
 
 ROCKETPORT EXPRESS/INFINITY DRIVER
···
 M:	Jiri Slaby <[e-mail]>
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
-F:	Documentation/serial/
+F:	Documentation/driver-api/serial/
 F:	drivers/tty/
 F:	drivers/tty/serial/serial_core.c
 F:	include/linux/serial_core.h

drivers/tty/Kconfig

···
 	  This driver supports Comtrol RocketPort and RocketModem PCI boards.   
           These boards provide 2, 4, 8, 16, or 32 high-speed serial ports or
           modems.  For information about the RocketPort/RocketModem  boards
-          and this driver read <file:Documentation/serial/rocket.rst>.
+          and this driver read <file:Documentation/driver-api/serial/rocket.rst>.
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called rocket.
···
 	  your Linux box, for instance in order to become a dial-in server.
 
 	  For information about the Cyclades-Z card, read
-	  <file:Documentation/serial/cyclades_z.rst>.
+	  <file:Documentation/driver-api/serial/cyclades_z.rst>.
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called cyclades.

drivers/tty/serial/ucc_uart.c

···
 }
 /* UART operations
  *
- * Details on these functions can be found in Documentation/serial/driver.rst
+ * Details on these functions can be found in Documentation/driver-api/serial/driver.rst
  */
 static const struct uart_ops qe_uart_pops = {
 	.tx_empty       = qe_uart_tx_empty,

include/linux/serial_core.h

···
 
 /*
  * This structure describes all the operations that can be done on the
- * physical hardware.  See Documentation/serial/driver.rst for details.
+ * physical hardware.  See Documentation/driver-api/serial/driver.rst for details.
  */
 struct uart_ops {
 	unsigned int	(*tx_empty)(struct uart_port *);