drm/i915: Create generic functions to control RC6, RPS

drm/i915: Create generic functions to control RC6, RPS

Prepared generic functions intel_enable_rc6, intel_disable_rc6,
intel_enable_rps and intel_disable_rps functions to setup RC6/RPS
based on platforms.

v2: Make intel_enable/disable_rc6/rps static. (Chris)

v3: Added lockdep_assert_held(dev_priv->pcu_lock) in new generic
functions. (Chris)
Removed WARN_ON(&dev_priv->pcu_lock) from lower level functions as generic
function now has lockdep_assert. Rebase.

Signed-off-by: Sagar Arun Kamble <[email protected]>
Cc: Imre Deak <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Radoslaw Szwichtenberg <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Acked-by: Imre Deak <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]