ntsync: Introduce NTSYNC_IOC_WAIT_ANY.

This corresponds to part of the functionality of the NT syscall
NtWaitForMultipleObjects(). Specifically, it implements the behaviour where
the third argument (wait_any) is TRUE, and it does not handle alertable waits.
Those features have been split out into separate patches to ease review.

This patch therefore implements the wait/wake infrastructure which comprises the
core of ntsync's functionality.

NTSYNC_IOC_WAIT_ANY is a vectored wait function similar to poll(). Unlike
poll(), it "consumes" objects when they are signaled. For semaphores, this means
decreasing one from the internal counter. At most one object can be consumed by
this function.

This wait/wake model is fundamentally different from that used anywhere else in
the kernel, and for that reason ntsync does not use any existing infrastructure,
such as futexes, kernel mutexes or semaphores, or wait_event().

Up to 64 objects can be waited on at once. As soon as one is signaled, the
object with the lowest index is consumed, and that index is returned via the
"index" field.

A timeout is supported. The timeout is passed as a u64 nanosecond value, which
represents absolute time measured against either the MONOTONIC or REALTIME clock
(controlled by the flags argument). If U64_MAX is passed, the ioctl waits
indefinitely.

This ioctl validates that all objects belong to the relevant device. This is not
necessary for any technical reason related to NTSYNC_IOC_WAIT_ANY, but will be
necessary for NTSYNC_IOC_WAIT_ALL introduced in the following patch.

Some padding fields are added for alignment and for fields which will be added
in future patches (split out to ease review).

Signed-off-by: Elizabeth Figura <zfigura@codeweavers.com>
Link: https://lore.kernel.org/r/20241213193511.457338-4-zfigura@codeweavers.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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