arm: topology: Define arch_get_cpu_efficiency() API for scheduler

On a HMP system, scheduler needs to know efficiency factor
(instructions-per-cycle) for various cpus. This is so that scheduler
can estimate bandwidth consumption of tasks on each cpu, based on
their efficiency factor.

This patch defines arch_get_cpu_efficiency() API in ARM32 architecture.
It depends on hard-coded "efficiency" factor for various cpu types
(available in 'table_efficiency' data structure) and device-tree
providing information on cpu-type for every cpu.

Change-Id: I561bace8a813a35a9fc624fca4861c5b1109b69b
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>