usb: fotg210: Collect pieces of dual mode controller

The Faraday FOTG210 is a dual-mode OTG USB controller that can
act as host, peripheral or both. To be able to probe from one
hardware description and to follow the pattern of other dual-
mode controllers such as MUSB or MTU3 we need to collect the
two, currently completely separate drivers in the same
directory.

After this, users need to select the main symbol USB_FOTG210
and then each respective subdriver. We pave the road to
compile both drivers into the same kernel and select the
one we want to use at probe() time, and possibly add OTG
support in the end.

This patch doesn't do much more than create the new symbol
and collect the drivers in one place. We also add a comment
for the section of dual-mode controllers in the Kconfig
file so people can see what these selections are about.

Also add myself as maintainer as there has been little
response on my patches to these drivers.

Cc: Fabian Vogt <fabian@ritter-vogt.de>
Cc: Yuan-Hsin Chen <yhchen@faraday-tech.com>
Cc: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20221023144708.3596563-1-linus.walleij@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>