drm/i915: PSR VLV/CHV: Introduce setup, enable and disable functions

drm/i915: PSR VLV/CHV: Introduce setup, enable and disable functions

The biggest difference from HSW/BDW PSR here is that VLV enable_source
function enables PSR but let it in Inactive state. So it might be called
on early stage along with setup and enable_sink ones.

v2: Rebase over intel_psr.c;
    Remove docs from static functions;
    Merge vlv_psr_active_on_pipe;
    Timeout for psr transition is 250us;
    Remove SRC_TRASMITTER_STATE;

v3: Rebase after is_psr_enabled function got removed;
    Get SRC_TRANSMITTER_STATE back to be on the safe side since
    default for panels is to require link training on exit when
    main link off;
    As pointed out by Durgadoss msecs_to_jiffies used on wait_for only uses int,
    so let's use 1 instead. Althought the 1/4 of this is needed for the
    transition let's use 1 for simplicity;

Cc: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>