intel: Load the driver even if I915_PARAM_REVISION is not found.

intel: Load the driver even if I915_PARAM_REVISION is not found.

This param is only available starting on kernel 4.1. Use a default
value of 0 if it is not found instead.

v2: Update commit message (Lionel)

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Mark Janes <mark.a.janes@intel.com>
Fixes: 96e1c945f2b ("i965: Move device info initialization to common
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3727>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3727>