serial: 8250: remove Kconfig indirection

Remove CONFIG_SERIAL_DETECT_IRQ and CONFIG_SERIAL_MANY_PORTS, and
substitute all references to the proper 8250 Kconfig options.  Now, the
actual Kconfig dependencies are not hidden when reading the code and
static analyzers are less confused.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>