[hci] Allow tab key to be used to cycle through UI elements

[hci] Allow tab key to be used to cycle through UI elements

Add support for wraparound scrolling and allow the tab key to be used
to move forward through a list of elements, wrapping back around to
the beginning of the list on overflow.

This is mildly useful for a menu, and likely to be a strong user
expectation for an interactive form.

Signed-off-by: Michael Brown <mcb30@ipxe.org>