sunxi:axp20x: Enable internal thermal monitoring

Enable the internal thermal monitoring support of AXP20X chips

Cherry-picked from:

https://github.com/cubieboard/linux-sunxi/commit/e4144b3ce62b1d7014fee36b84bc65c812469822

Creates the sysfs file temp1_input in the sunxi-i2c tree that reports the
AXP's temperature in degrees C.

According to the AXP202's datasheet, this port outputs a 12-bit value
where 0x000 == -144.7C and 0xfff == 264.8C in 0.1 degree C increments.

Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Patrick Wood <patrickhwood@gmail.com>
arm:sunxi:defconfig: enable HWMON

Signed-off-by: Alejandro Mery <amery@geeks.cl>