Before moving greybus core out of staging and moving header files to
include/linux some greybus header files were missing the necessary
includes. This would trigger compilation faillures with some example
errors logged bellow for with CONFIG_KERNEL_HEADER_TEST=y.

So, add the necessary headers to compile clean before relocating the
header files.

./include/linux/greybus/hd.h:23:50: error: unknown type name 'u16'
  int (*cport_disable)(struct gb_host_device *hd, u16 cport_id); ^~~
./include/linux/greybus/greybus_protocols.h:1314:2: error: unknown type name '__u8'
  __u8 data[0];
  ^~~~
./include/linux/greybus/hd.h:24:52: error: unknown type name 'u16'
  int (*cport_connected)(struct gb_host_device *hd, u16 cport_id); ^~~
./include/linux/greybus/hd.h:25:48: error: unknown type name 'u16'
  int (*cport_flush)(struct gb_host_device *hd, u16 cport_id); ^~~
./include/linux/greybus/hd.h:26:51: error: unknown type name 'u16'
  int (*cport_shutdown)(struct gb_host_device *hd, u16 cport_id, ^~~
./include/linux/greybus/hd.h:27:5: error: unknown type name 'u8'
u8 phase, unsigned int timeout);
     ^~
./include/linux/greybus/hd.h:28:50: error: unknown type name 'u16'
  int (*cport_quiesce)(struct gb_host_device *hd, u16 cport_id, ^~~
./include/linux/greybus/hd.h:29:5: error: unknown type name 'size_t'
     size_t peer_space, unsigned int timeout);
     ^~~~~~
./include/linux/greybus/hd.h:29:5: note: 'size_t' is defined in header '<stddef.h>'; did you forget to '#include <stddef.h>'?
./include/linux/greybus/hd.h:1:1:
+#include <stddef.h>
 /* SPDX-License-Identifier: GPL-2.0 */
./include/linux/greybus/hd.h:29:5:
     size_t peer_space, unsigned int timeout);
     ^~~~~~
./include/linux/greybus/hd.h:30:48: error: unknown type name 'u16'
  int (*cport_clear)(struct gb_host_device *hd, u16 cport_id); ^~~
./include/linux/greybus/hd.h:32:49: error: unknown type name 'u16'
  int (*message_send)(struct gb_host_device *hd, u16 dest_cport_id, ^~~
./include/linux/greybus/hd.h:33:32: error: unknown type name 'gfp_t'
struct gb_message *message, gfp_t gfp_mask); ^~~~~
./include/linux/greybus/hd.h:35:55: error: unknown type name 'u16'
  int (*latency_tag_enable)(struct gb_host_device *hd, u16 cport_id);
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Gao Xiang <hsiangkao@aol.com>
Signed-off-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Link: https://lore.kernel.org/r/20190827155302.25704-1-rui.silva@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>