arch: remove frv port

arch: remove frv port

The Fujitsu FRV kernel port has been around for a long time, but has not
seen regular updates in several years and instead was marked 'Orphaned'
in 2016 by long-time maintainer David Howells.

The SoC product line apparently is apparently still around in the form
of the Socionext Milbeaut image processor, but this one no longer uses
the FRV CPU cores.

This removes all FRV specific files from the kernel.

Link: http://www.socionext.com/en/products/assp/milbeaut/
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>