drm/i915/guc: Redefine guc_log_level modparam values

We used value -1 to indicate "disabled" and values 0..3 to
indicate "enabled", but most of our other modparams are using
-1 for "auto" mode and 0 for "disable". For consistency let's
change our log level values to:

-1: auto (depends on platform and Kconfig.debug settings)
 0: disabled
 1: enabled (severity level 0 = min)
 2: enabled (severity level 1)
 3: enabled (severity level 2)
 4: enabled (severity level 3 = max)

v2: fix commit message (Sagar)
    display sanitized modparam value (Sagar)
    unify sanitize messages (Sagar/Michal)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180111152441.21676-1-michal.wajdeczko@intel.com
Reviewed-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>