x86/headers/UAPI: Use __u64 instead of u64 in <uapi/asm/hyperv.h>

... since u64 has a hidden header dependency that was not there before
using it (i.e. it breaks our VMM build).

Also, __u64 is the right way to expose data types through UAPI.

Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: devel@linuxdriverproject.org
Fixes: 93286261 ("x86/hyperv: Reenlightenment notifications support")
Link: http://lkml.kernel.org/r/1519112391-23773-1-git-send-email-karahmed@amazon.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>