swiotlb: using SIZE_MAX needs limits.h included

swiotlb: using SIZE_MAX needs limits.h included

After merging the drm-misc tree, linux-next build (arm
multi_v7_defconfig) failed like this:

In file included from drivers/gpu/drm/nouveau/nouveau_ttm.c:26:
include/linux/swiotlb.h: In function 'swiotlb_max_mapping_size':
include/linux/swiotlb.h:99:9: error: 'SIZE_MAX' undeclared (first use in this function)
   99 |  return SIZE_MAX;
      |         ^~~~~~~~
include/linux/swiotlb.h:7:1: note: 'SIZE_MAX' is defined in header '<stdint.h>'; did you forget to '#include <stdint.h>'?
    6 | #include <linux/init.h>
  +++ |+#include <stdint.h>
    7 | #include <linux/types.h>
include/linux/swiotlb.h:99:9: note: each undeclared identifier is reported only once for each function it appears in
   99 |  return SIZE_MAX;
      |         ^~~~~~~~

Caused by commit

  abe420bfae52 ("swiotlb: Introduce swiotlb_max_mapping_size()")

but only exposed by commit "drm/nouveu: fix swiotlb include"

Fix it by including linux/limits.h as appropriate.

Fixes: abe420bfae52 ("swiotlb: Introduce swiotlb_max_mapping_size()")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/r/20201102124327.2f82b2a7@canb.auug.org.au
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>