Exports pcc_mbox_request_channel() and pcc_mbox_free_channel()
declarations into a pcc.h header file.

Looks-good-to: Prashanth Prakash <pprakash@codeaurora.org>
Signed-off-by: NHoan Tran <hotran@apm.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Remove a redundant function declaration in cppc_acpi.h for
mbox_send_message().  That function is defined in mailbox_client.h,
which is already included.
Signed-off-by: NTimur Tabi <timur@codeaurora.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

CPPC stands for Collaborative Processor Performance Controls
and is defined in the ACPI v5.0+ spec. It describes CPU
performance controls on an abstract and continuous scale
allowing the platform (e.g. remote power processor) to flexibly
optimize CPU performance with its knowledge of power budgets
and other architecture specific knowledge.

This patch adds a shim which exports commonly used functions
to get and set CPPC specific controls for each CPU. This enables
CPUFreq drivers to gather per CPU performance data and use
with exisiting governors or even allows for customized governors
which are implemented inside CPUFreq drivers.
Signed-off-by: NAshwin Chaugule <ashwin.chaugule@linaro.org>
Reviewed-by: NAl Stone <al.stone@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>