tty: serial: meson: if no alias specified use an available id

[ Upstream commit a26988e8fef4b258d1b771e0f4b2e3b67cb2e044 ]

At probe, the uart driver tries to get an id from a device tree alias.
When no alias was specified, the driver would return an error and probing
would fail.

Providing an alias for registering a serial device should not be mandatory.
If the device tree does not specify an alias, provide an id from a reserved
range so that the probing can continue.

Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Loys Ollivier <lollivier@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 2a1d728f20ed ("tty: serial: meson: fix hard LOCKUP on crtscts mode")
Signed-off-by: Sasha Levin <sashal@kernel.org>