remoteproc: Move resource table load logic to find

Extend the previous operation of finding the resource table in the ELF
with the extra step of populating the rproc struct with a copy and the
size. This allows drivers to override the mechanism used for acquiring
the resource table, or omit it for firmware that is known not to have a
resource table.

This leaves the custom, dummy, find_rsc_table implementations found in
some drivers dangling.

Reviewed-By: Loic Pallardy <loic.pallardy@st.com>
Tested-By: Loic Pallardy <loic.pallardy@st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>