drm/i915/tgl: Remove require_force_probe protection

We have a few TGL machines in our CI and it is mostly green with
failures in tests that will not impact future Linux installations.
Also there is no warnings, errors, flickering or any visual defects
while doing ordinary tasks like browsing and editing documents in a
dual monitor setup.

As a reminder i915.require_force_probe was created to protect
future Linux installation's iso images that might contain a
kernel from the enabling time of the new platform. Without this
protection most of linux installation was recommending
nomodeset option during installation that was getting stick
there after installation.

Reference: https://intel-gfx-ci.01.org/tree/drm-tip/fi-tgl-u.html
Reference: https://intel-gfx-ci.01.org/tree/drm-tip/shard-tglb.html
Cc: James Ausmus <james.ausmus@intel.com>
Cc: Jani Saarinen <jani.saarinen@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200218230822.66801-1-jose.souza@intel.com