drm/i915: Set up PIPE_MISC truncate bit on tgl+

Looks like the pipe rounding mode bit has moved from PIPE_CHICKEN to
PIPE_MISC on tgl. Frob the new location.

Bspec does still document the old bits as well, so I left the code
for them as is until we get clarification from the hw folks on
whether the old bits still do something useful.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226163054.9509-1-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>