serial: lpuart: Avoid division by zero when requested baudrate is ...

With serdev device support added there's now a corner case where:

 1. There is a DT node for a serdev device on one of the UARTs
 2. There is no driver that binds against serdev device's compatibility
    string

with 1 and 2 being true it is possible to end up in a situation where
a particualr UART has not been initalized to any baudrate when
clock_notifier_call_chain() gets called. This effectively translates
to

	set_baudrate(uart, 0);

which for LPUART driver result in a division by zero.

To avoid this problem, convert lpuart_serial_setbaudrate() to treat
zero baudrate as a request to disable the UART. While we are at it add
a BUG_ON() to lpuart_setbrg() to simplify finding any future bugs.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Merge branch 'for-next/serdev'

serial: Drop .remove functions from all drivers ...

Depending on specifics, some 'serdev' devices might need prevent
parent console device from being removed and corresponding memory
deallocated to properly function until the very end of Barebox's
execution. An example of such a use-case would be a reset handler
relying on a serdev device for transport.

To avoid having to develop complicatione reference counting/ownership
scheme drop all of the code that calls console_unregister() and frees
the memory effectively making the problem above impossible to arise.

All of the de-initialization that serial drivers were doing in their
.remove functions was somewhat superflous anyway, so this change
should be pretty harmless.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

serial/lpuart: Do not enable UART FIFO ...

Using FIFO in LPUART results in subtle serial input draining issues
which are quite difficult to reproduce and troubleshoot. Since the
change offered only moderate performance gain revert the code to
operate in no-FIFO mode to avoid FIFO-related problems alltogether.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

i.MX: Add 'lpuart' serial driver ...

Add 'lpuart' serial driver, based on analogous driver from U-Boot

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>