remoteproc: Calculate max_notifyid during load

The calculation of max_notifyid must only be done before we call start()
on the remoteproc drivers, so move the calculation to be part of the
loading steps.

Cc: Lee Jones <lee.jones@linaro.org>
Cc: Loic Pallardy <loic.pallardy@st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>