net: wan: framer: Add support for the Lantiq PEF2256 framer

The Lantiq PEF2256 is a framer and line interface component designed to
fulfill all required interfacing between an analog E1/T1/J1 line and the
digital PCM system highway/H.100 bus.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20231128132534.258459-4-herve.codina@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

net: wan: Add framer framework support

A framer is a component in charge of an E1/T1 line interface.
Connected usually to a TDM bus, it converts TDM frames to/from E1/T1
frames. It also provides information related to the E1/T1 line.

The framer framework provides a set of APIs for the framer drivers
(framer provider) to create/destroy a framer and APIs for the framer
users (framer consumer) to obtain a reference to the framer, and
use the framer.

This basic implementation provides a framer abstraction for:
- power on/off the framer
- get the framer status (line state)
- be notified on framer status changes
- get/set the framer configuration

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20231128132534.258459-2-herve.codina@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>