x86/platform/uv/BAU: Add payload descriptor qualifier

x86/platform/uv/BAU: Add payload descriptor qualifier

On UV4, the destination agent verifies each message by checking the
descriptor qualifier field of the message payload. Messages without this
field set to 0x534749 will cause a hub error to assert. Split
bau_message_payload into uv1_2_3 and uv4 versions to account for the
different payload formats.

Enforce the size of each field by using the appropriate u** integer type.
Replace extraneous comments with KernelDoc comment.

Signed-off-by: Andrew Banman <abanman@hpe.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Mike Travis <mike.travis@hpe.com>
Cc: sivanich@hpe.com
Cc: rja@hpe.com
Cc: akpm@linux-foundation.org
Link: http://lkml.kernel.org/r/1489077734-111753-3-git-send-email-abanman@hpe.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>