FROMLIST: 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].

The `ktime_get` method 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.

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]
Bug: 330152405
Link: https://lore.kernel.org/r/20240322-rust-ktime_ms_delta-v2-1-d98de1f7c282@google.com


Change-Id: I3c07fa97178d05b9c3a7c19030724fc13bce0744
Signed-off-by: Alice Ryhl <aliceryhl@google.com>