drm/i915: Drop has_rc6 from device info

No need to have this parameter in intel_device_info struct
as all platforms with graphics version 6 or newer have software
support for this feature.

As a side effect of the of removal this flag, it will not be printed
in dmesg during driver load anymore and developers will have to rely
on to check the macro and compare with platform being used and IP
versions of it.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505193524.276400-2-jose.souza@intel.com