rv/monitors: Move monitor structure in rodata

It makes sense to move the important monitor structure into rodata to
prevent accidental structure modification.

Link: https://lkml.kernel.org/r/20221122173648.4732-1-acarmina@redhat.com

Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>