rust: time: Add Ktime

Introduce a wrapper around `ktime_t` with a few different useful methods.

Rust Binder will use these bindings to compute how many milliseconds a
transaction has been active for when dumping the current state of the
Binder driver. This replicates the logic in C Binder [1].

For a usage example in Rust Binder, see [2].

ktime_get() cannot be safely called in NMI context. This requirement is not
checked by these abstractions, but it is intended that klint [3] or a
similar tool will be used to check it in the future.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20240322-rust-ktime_ms_delta-v2-1-d98de1f7c282@google.com
Link: https://lore.kernel.org/lkml/5ac8c0d09392290be789423f0dd78a520b830fab.1682333709.git.zhangchuang3@xiaomi.com/ [1]
Link: https://r.android.com/3004103 [2]
Link: https://rust-for-linux.com/klint [3]

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