timekeeping: fix 32-bit overflow in get_monotonic_boottime

get_monotonic_boottime adds three nanonsecond values stored
in longs, followed by an s64.  If the long values are all
close to 1e9 the first three additions can overflow and
become negative when added to the s64.  Cast the first
value to s64 so that all additions are 64 bit.

Change-Id: Ic996d8b6fbef0b72f2d027b0d8ef5259b5c1a540
Signed-off-by: Colin Cross <ccross@android.com>
ARM: disable preemption in machine_shutdown

Since the smp call to stop the other cpus are handled in those
cpus in interrupt context, there's a potential for those smp
handlers to interrupt threads holding spin locks (such as the
one a mutex holds).  This prevents those threads from ever
releasing their spin lock, so if the cpu doing the shutdown
is allowed to switch to another thread that tries to grab the
same lock/mutex, we could get into a deadlock (the spin lock
call is called with preemption disabled in the mutex lock code).

To avoid that possibility, disable preemption before doing the
smp_send_stop().

Change-Id: I7976c5382d7173fcb3cd14da8cc5083d442b2544
Signed-off-by: Mike J. Chen <mjchen@google.com>