of: Don't create device for OPP tables

The OPP tables are present as separate nodes, whose phandle is used in
the "operating-points-v2" property of devices. Currently the OF core
creates a device for the OPP table unconditionally, which is not used by
any kernel code.

This patch creates another OF device_id table for the nodes which must
be skipped while creating devices and OPP is the only user of it for now.

Reported-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>