Use tools/build/ makefiles to build rv, inheriting the benefits of
it. For example, having a proper way to handle dependencies.

Link: https://lkml.kernel.org/r/2a38a8f7b8dc65fa790381ec9ab42fb62beb2e25.1710519524.git.bristot@kernel.org

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: John Kacur <jkacur@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>