drm/i915/csr: alpha_support doesn't depend on csr or vice versa

Debug logging should not be dependent on alpha support flag.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190429142253.15882-1-jani.nikula@intel.com