arm: topology: Allow specifying the CPU efficiency from device tree

The efficiency of a CPU can vary across SoCs depending on the
cache size, bus interconnect frequencies etc. Allow specifying
this from the device tree. This value overrides the default
values hardcoded in the efficiency table.

Change-Id: If2885675ce3d7b43c3b2568fe1e29a76f48a5c3d
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>