arch: remove m32r port

The Mitsubishi/Renesas m32r architecture has been around for many years,
but the Linux port has been obsolete for a very long time as well, with
the last significant updates done for linux-2.6.14.

While some m32r microcontrollers are still being marketed by Renesas,
those are apparently no longer possible to support, mainly due to the
lack of an external memory interface.

Hirokazu Takata was the maintainer until the architecture got marked
Orphaned in 2014.

Link: http://www.linux-m32r.org/
Link: https://www.renesas.com/en-eu/products/microcontrollers-microprocessors/m32r.html


Cc: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>