drm/i915: Deduplicate register definition for GAMW_ECO_DEV_RW_IA

This got duplicated on introducing icl workarounds.
Fix by using the older definition and moving the wa bit
definition there. No functional changes.

v3: avoid fixes tag, whitespace (Chris)

References: 908ae051 ("drm/i915/icl: WaDisCtxReload")
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20181109145333.10570-1-mika.kuoppala@linux.intel.com