cmds/hwclock: add initial implementation
cmds/hwclock: add initial implementation

Add a simple hwclock implementation based on u-root's rtc pkg. It
supports reading and settting the hardware clock. Its output format
matches the one of util-linux' hwclock implementation.

Fixes #982

Co-authored-by: claudiozz <99ee8c1549150ecb773cbad4942ffe7c0fe3b45e@gmail.com>
Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>

u-root/u-root,u-root/u-root,hugelgupf/u-root,hugelgupf/u-root,u-root/u-root,hugelgupf/u-root,GanShun/u-root,GanShun/u-root,GanShun/u-root,hugelgupf/u-root