i965/gen8: Initialize aux_mode to GEN8_SURFACE_AUX_MODE_NONE

i965/gen8: Initialize aux_mode to GEN8_SURFACE_AUX_MODE_NONE

GEN8_SURFACE_AUX_MODE_NONE is 0, so this is a no-op.

Yet, this also makes it clear that we can compare aux_mode to the
other GEN8_SURFACE_AUX_MODE_ values. We will want to compare to
GEN8_SURFACE_AUX_MODE_HIZ.

v2: Some very minor cherry-pick conflicts due to moving it around in the series.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Ben Widawsky <benjamin.widawsky@intel.com>
Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>