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.

CRs-Fixed: 1003878
Change-Id: If2885675ce3d7b43c3b2568fe1e29a76f48a5c3d
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>