drm/i915/display: Move HAS_LT_PHY() to intel_display_device.h

drm/i915/display: Move HAS_LT_PHY() to intel_display_device.h

We will need to HAS_LT_PHY() that macro in code outside of LT PHY
implementation. Move its definition to intel_display_device.h.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20251202012306.9315-8-matthew.s.atwood@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>