serial: general fixes in the serial_rs485 structure

Fix several issues related to the RS485 interface:

 - It adds the flag SER_RS485_RTS_BEFORE_SEND that was missing from the
   serial_rs485 structure (even if "delay_rts_before_send" was existing)

 - It adds a further "delay_rts_after_send" field for those drivers that
   can have a delay after send (e.g., atmel_serial)

 - It fixes the usage of the structure in the atmel_serial driver (where
   "delay_rts_before_send" should be used instead of "delay_rts_after_send").

Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Signed-off-by: Bernhard Roth <br@pwrnet.de>
Cc: Philippe De Muyter <phdm@macqel.be>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>