drm/i915: Clean up various HPD defines

Indent the PORTx_HOTPLUG_... defines appropriately, and fix some space
vs. tab issues.

v2: Document pre-HSW/LPT bits, and order another tab (Paulo)

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>