qga: move linux disk/cpu stats command impls to commands-linux.c

qga: move linux disk/cpu stats command impls to commands-linux.c

The qmp_guest_{diskstats,cpustats} command impls in
commands-posix.c are surrounded by '#ifdef __linux__' so should
instead live in commands-linux.c

This also removes a "#ifdef CONFIG_LINUX" that was nested inside
a "#ifdef __linux__".

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-ID: <20240712132459.3974109-6-berrange@redhat.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>