drm/i915/tgl: Enable DC3CO state in "DC Off" power well

Add target_dc_state and used by set_target_dc_state API
in order to enable DC3CO state with existing DC states.
target_dc_state will enable/disable the desired DC state in
DC_STATE_EN reg when "DC Off" power well gets disable/enable.

v2: commit log improvement.
v3: Used intel_wait_for_register to wait for DC3CO exit. [Imre]
    Used gen9_set_dc_state() to allow/disallow DC3CO. [Imre]
    Moved transcoder psr2 exit line enablement from tgl_allow_dc3co()
    to a appropriate place haswell_crtc_enable(). [Imre]
    Changed the DC3CO power well enabled call back logic as
    recommended in review comments. [Imre]
v4: Used wait_for_us() instead of intel_wait_for_reg(). [Imre (IRC)]
v5: using udelay() instead of waiting for DC3CO exit status.
v6: Fixed minor unwanted change.
v7: Removed DC3CO powerwell and POWER_DOMAIN_VIDEO.
v8: Uniform checks by using only target_dc_state instead of allowed_dc_mask
    in "DC off" power well callback. [Imre]
    Adding "DC off" power well id to older platforms. [Imre]
    Removed psr2_deep_sleep flag from tgl_set_target_dc_state. [Imre]
v9: Used switch case for target DC state in
    gen9_dc_off_power_well_disable(), checking DC3CO state against
    allowed DC mask, using WARN_ON() in
    tgl_set_target_dc_state(). [Imre]
v10: Code refactoring and using sanitize_target_dc_state(). [Imre]

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191003081738.22101-4-anshuman.gupta@intel.com