tty: serial: 8250: Remove SERIAL_DEBUG_PNP macro

This patch removes the macro SERIAL_DEBUG_PNP, which is used to enable
debugging at compile time.
As SERIAL_DEBUG_PNP is an orphan, the corresponding #ifdef is removed.
To keep the ability to enable debugging at compile time,
the call to printk(KERN_DEBUG ...) is replaced by a corresponding
call to dev_dbg(), which is configurable via CONFIG_DYNAMIC_DEBUG.

Signed-off-by: Phillip Raffeck <phillip.raffeck@fau.de>
Signed-off-by: Anton Würfel <anton.wuerfel@fau.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: linux-kernel@i4.cs.fau.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>