For cases where sys mapped CPC registers need to be accessed
frequently, it helps immensly to pre-map them rather than map
and unmap for each operation. e.g. case where feedback counters
are sys mem map registers.

Restructure cpc_read/write and the cpc_regs structure to allow
pre-mapping the system addresses and unmap them when the CPU exits.
Signed-off-by: NAshwin Chaugule <ashwin.chaugule@linaro.org>
Signed-off-by: NPrashanth Prakash <pprakash@codeaurora.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>