hwclock: make RTC default to UTC time

hwclock: make RTC default to UTC time

If /etc/adjtime doesn't specify UTC or LOCAL, rtcwake defaults to UTC
and hwclock defaults to LOCAL.

Switch hwclock to meet the behaviour of rtcwake (default=UTC), also
matching the kernel's CONFIG_RTC_HCTOSYS behaviour.

The user impact of this change should be minimal, as anyone who has run
"hwclock --systohc" before will have their UTC/LOCAL choice already
recorded in /etc/adjtime.

Signed-off-by: Daniel Drake <dsd@laptop.org>