arm64: 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: Ie9ba69e11317e6eb6462630226355747d1def646
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>