drm/i915/tgl: Implement Wa_1604555607

Implement Wa_1604555607 (set the DS pairing timer to 128 cycles).
FF_MODE2 is part of the register state context, that's why it is
implemented here.

At TGL A0 stepping, FF_MODE2 register read back is broken, hence
disabling the WA verification.

v2: Rebased on top of the WA refactoring (Oscar)
v3: Correctly add to ctx_workarounds_init (Michel)
v4:
  uncore read is used [Tvrtko]
  Macros as used for MASK definition [Chris]
v5:
  Skip the Wa_1604555607 verification [Ram]
  i915 ptr retrieved from engine. [Tvrtko]
v6:
  Added wa_add as a wrapper for __wa_add [Chris]
  wa_add is directly called instead of new wrapper [tvrtko]

BSpec: 19363
HSDES: 1604555607
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Ramalingam C <ramlingam.c@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> [v5]
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191128021005.3350-1-ramalingam.c@intel.com