Initial support for Allwinner's Security ID fuses

Allwinner has electric fuses (efuse) on their line of chips. This driver
reads those fuses, seeds the kernel entropy and exports them as a sysfs
node.

These fuses are most likely to be programmed at the factory, encoding
things like Chip ID, some sort of serial number etc and appear to be
reasonable unique.
While in theory, these should be writeable by the user, it will probably
be inconvinient to do so. Allwinner recommends that a certain input pin,
labeled 'efuse_vddq', be connected to GND. To write these fuses however,
a 2.5 V programming voltage needs to be applied to this pin.

Even so, they can still be used to generate a board-unique mac from,
board unique RSA key and seed the kernel RNG.

On sun7i additional storage is available, this is initially used for an
UEFI BOOT key, Secure JTAG key, HDMI-HDCP key and vendor specific keys.

Currently supported are the following known chips:
Allwinner sun4i (A10)
Allwinner sun5i (A10s, A13)
Allwinner sun7i (A20)

Signed-off-by: Oliver Schinagl <oliver@schinagl.nl>
Add sunxi-sid to dts for sun4i, sun5i and sun7i

This patch shall add support for the sunxi-sid driver to the device
tree for A10, A10s, A13 and A20.

Signed-off-by: Oliver Schinagl <oliver@schinagl.nl>