PM / devfreq: exynos: Add support of bus frequency of sub-blocks using passive governor

PM / devfreq: exynos: Add support of bus frequency of sub-blocks using passive governor

This patch adds the support of bus frequency feature for sub-blocks which share
the one power line. If each bus depends on the power line, each bus is not able
to change the voltage by oneself. To optimize the power-consumption on runtime,
some buses using the same power line should change the source clock and
regulator at the same time. So, this patch uses the passive governor to support
the bus frequency for all buses which sharing the one power line.

For example,

Exynos3250 include the two power line for AXI buses as following:
: VDD_MIF : MIF (Memory Interface) provide the DMC (Dynamic Memory Controller)
  with the power (regulator).
: VDD_INT : INT (Internal) provide the various sub-blocks with the power
  (regulator).

Each bus is included in as follwoing block. In the case of VDD_MIF, only DMC bus
use the power line. So, there is no any depencency between buese. But, in the
case of VDD_INT, various buses share the one power line of VDD_INT. We need to
make the depenency between buses. When using passive governor, there is no
problem to support the bus frequency as DVFS for all buses. One bus should be
operated as the parent bus device which gathering the current load of INT block
and then decides the new frequency with some governors except of passive
governor. After deciding the new frequency by the parent bus device, the rest
bus devices will change the each source clock according to new frequency of the
parent bus device.

- MIF (Memory Interface) block
: VDD_MIF |--- DMC

- INT (Internal) block
: VDD_INT |--- LEFTBUS (parent)
          |--- PERIL
          |--- MFC
          |--- G3D
          |--- RIGHTBUS
          |--- FSYS
          |--- LCD0
          |--- PERIR
          |--- ISP
          |--- CAM

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
[tjakobi: Reported debugfs error during booting and cw00.choi fix it.]
Reported-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Acked-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>