serial: rewrite pxa2xx-uart to use 8250_core

pxa2xx-uart was a separate uart platform driver. It was declaring
the same device names and numbers as 8250 driver. As a result,
it was impossible to use 8250 driver on PXA SoCs.

Upon closer examination pxa2xx-uart turned out to be a clone of
8250_core driver.

Workaround for Erratum #19 according to Marvel(R) PXA270M Processor
Specification Update (April 19, 2010) is dropped. 8250_core reads
from FIFO immediately after checking DR bit in LSR.

The patch leaves the original SERIAL_PXA driver around. The original
driver is just marked DEPRECATED in Kconfig and C source. When
the original driver is considered safe to remove, no changes
to SERIAL_8250 will be necessary.

Compiling SERIAL_8250_CONSOLE and SERIAL_PXA_CONSOLE even without
SERIAL_8250_PXA breaks console for SERIAL_PXA. For this reasons, the new
and the original drivers are made mutually exclusive.

Signed-off-by: Sergei Ianovich <ynvich@gmail.com>
CC: Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC: James Cameron <quozl@laptop.org>
CC: Robert Jarzmik <robert.jarzmik@free.fr>
CC: Russell King <linux@arm.linux.org.uk>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
[rebased on v4.8]
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>