MFC r360140, r360155: kqueue timer/data fixes

r360140:
kqueue: fix conversion of timer data to sbintime

This unbreaks the i386 kqueue timer tests after a recent change switched
NOTE_ABSTIME over to using microseconds. Notably, the data argument (which
holds useconds) is an int64_t, but we were passing it to timer2sbintime
which takes an intptr_t. Perhaps in a previous incarnation, intptr_t would
have made sense, but now it just leads to the timestamp getting truncated
and subsequently rejected when it no longer fits in an intptr_t.

r360155:
kevent32: fix the split of data into data1/data2

The current situation results in intermittent breakage if data gets split up
with the sign bit set on the data1 half of it, as PAIR32TO64 will then:
data1 | (data2 << 32) -> resulting in data1 getting sign-extended when it's
implicitly widened and clobbering the result. AFAICT, there's no compelling
reason for these to be signed.

This was most exposed by flakiness in the kqueue timer tests under compat32
after the ABSTIME test got switched over to using a better clock and
microseconds.