staging: tidspbridge: remove rmm_init() and rmm_exit()

The rmm module has a rmm_init() and a rmm_exit() whose only purpose is
to keep a reference counting which is not used at all.

This patch removes these functions and the reference count variable.

There is no functional changes.

Signed-off-by: Víctor Manuel Jáquez Leal <vjaquez@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>