drivers/gpu/pvr/pvr_governor: add a simple PVR GPU governor

this simple PVR GPU governor will scale between 3 speeds:
  idle -- GPU not active
  nominal -- GPU active with low graphical load
  turbo -- GPU active and boosted to max frequency

This should further save battery by intelligently selecting GPU frequency
based on GPU loading.

Signed-off-by: Paul Reioux <reioux@gmail.com>
drivers/gpu/pvr/pvr_governor: add sysfs entry to switch governor type

0 - "performance" ==> always return system turbo speed
1 - "ondemand" ==> return based on GPU loading (by default "ondemand"
governor is active)

Signed-off-by: Paul Reioux <reioux@gmail.com>
drivers/gpu/pvr/pvr_governor: add "powersave" governor as another option

    0 - "performance" ==> always return system turbo speed
    1 - "ondemand" ==> return based on GPU loading (by default "ondemand"
                       governor is active)
    2 - "powersave" ==> run alway at nominal speed

Signed-off-by: Paul Reioux <reioux@gmail.com>
drivers/gpu/pvr/pvr_governor: fix sysfs to show "powersave" governor

Signed-off-by: Paul Reioux <reioux@gmail.com>
drivers/gpu/pvr/pvr_governor: add sysfs interface for current GPU freqeuncy

Signed-off-by: Paul Reioux <reioux@gmail.com>
Enable PVR GOVERNOR and tweaks