drm/i915: remove unused IO_TLB_SEGPAGES which should be defined by swiotlb

This patch removes IO_TLB_SEGPAGES which is no longer used since
commit 5584f1b1 ("drm/i915: fix i915 running as dom0 under Xen").

As the define of both IO_TLB_SEGSIZE and IO_TLB_SHIFT are from swiotlb,
IO_TLB_SEGPAGES should be defined on swiotlb side if it is required in the
future.
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1558413639-22568-1-git-send-email-dongli.zhang@oracle.com

drivers/gpu/drm/i915/i915_gem_internal.c

@@ -28,9 +28,6 @@
 #define QUIET (__GFP_NORETRY | __GFP_NOWARN)
 #define MAYFAIL (__GFP_RETRY_MAYFAIL | __GFP_NOWARN)
 
-/* convert swiotlb segment size into sensible units (pages)! */
-#define IO_TLB_SEGPAGES (IO_TLB_SEGSIZE << IO_TLB_SHIFT >> PAGE_SHIFT)
-
 static void internal_free_pages(struct sg_table *st)
 {
 	struct scatterlist *sg;