sunxi: Add axp152 pmic support

Add support for the x-powers axp152 pmic which is found on most A10s boards
and enable it for the r7-tv-dongle board.

Signed-off-by: Henrik Nordstrom <henrik@henriknordstrom.net>
Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>