drm/i915: remove transcoder PLL mashing from mode_set per specs

Belongs in PCH enable instead.  The duplication is worrying and the
specs explicitly list transcoder select *after* actual PLL enable, which
doesn't occur until later.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-By: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-By: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>