[kernel][x64][arm64] Add ability to shutdown platform timer

As part of the work to gracefully shutdown CPUs, we need to disable
the CPU's platform timer before powering it down.

This change adds platform_shutdown_timer(), which on arm64 masks the
interrupt and on x64 currently does nothing.

Nothing currently calls platform_shutdown_timer(). It will get wired
into the shutdown sequence in a future change.

Tested: Manually tested arm64 on qmeu using a separate change that
actually calls platform_shutdown_timer as part of shutting down
secondary CPUs.

ZX-2302 #comment prereq

ZX-2228 #comment prereq

Change-Id: I23df7c5b0c6b723b07b0ceccc0855b67de400470

[kernel][interrupts] Replace "enum handler_return" type with void

Following recent changes for using preempt_disable, all of the
in-kernel interrupt handlers now always return INT_NO_RESCHEDULE. We
can therefore remove their return values. We can use "void" instead
of "enum handler_return".

The bulk changes are:

* Search-and-replace "enum handler_return" -> "void".
* Manually change "return INT_NO_RESCHEDULE;" -> "return;", or remove
when at the end of a function.
* Manually change "return foo();" -> "foo();" when return type is
void (just a cleanup -- the code compiles without this change).

The non-bulk changes include:

* Remove the definition of enum handler_return.
* Update the interrupt entry points: faults.cpp and exceptions_c.cpp.
* Update a few places where handler_return values were propagated,
such as "handler->handler()" calls, removing "ret =".

Note that platform_fiq() (changed here) is called from ARM assembly.

ZX-1490

Change-Id: I70b57c610ded0facb93c09ac8ffc81cf23a985fc

[kernel][status] Migrate the rest to zx_status_t

Change-Id: If0a5d3e04bfc3e2a57d068350ee1d1156ed67872

[kernel][time] Prefer zx_{time,duration}_t to lk_time_t

Change-Id: Ie219c61f2ba7fd073917a6738221e2dde969fc2d

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[kernel][timer] simplify the hw timer setting api

Remove the need to pass a callback and arg, which were always pointing
at timer_tick() anyway.

Change-Id: Iac3663796105857e76309b01409bf2006403459b

[kernel][timers] remove periodic timer support

It's largely unused and adds some amount of complexity to the kernel
timer path which is going to be hard to maintain going forward.

Change-Id: Id9e3ae76bcb19857668ef690edc1646b3812e6c1

[kernel][timer] Remove non-dynamic timer from magenta.

MG-821 #done

Change-Id: I3e22dcfb4f72a702198c516be31f98037fdbdf60

[kernel][pc] Finish C++ conversion

Change-Id: Iea6ff5e497597c1b0cd3a914e1a3cdd5b641cf58

[kernel][time] Rename lk_bigtime_t and current_time_hires()

Now that millisecond time is gone from the kernel, reclaim the names
used for it.

lk_bigtime_t -> lk_time_t
current_time_hires() -> current_time()

Change-Id: I7db5de01171096c04a2b12d293e047e6a08a0aef

[kernel][time] Switch timeout interfaces to deadlines

This switches all kernel primitives to using deadlines with respect
to the monotonic clock instead of relative nanosecond timeouts.

The only remaining time interface that is not on deadlines is
thread_sleep.

Change-Id: Ibfb4e7a0673ecb5740dba33ee9d056f668e27256

[kernel][time] Switch kernel to nanoseconds internally

A subsequent diff will rename lk_bigtime_t to lk_time_t and
current_time_hires() to current_time().

Change-Id: Ied15e687714f784e2180aac59c8e0813c83bfcd0

[magenta] Initial commit