Abracon ABX80X I2C ultra low power RTC/Alarm chip

The Abracon ABX80X family consist of the ab0801, ab0803, ab0804, ab0805, ab1801,
ab1803, ab1804 and ab1805. The ab0805 is the superset of ab080x and the ab1805
is the superset of ab180x.

Required properties:

 - "compatible": should one of:
        "abracon,abx80x"
        "abracon,ab0801"
        "abracon,ab0803"
        "abracon,ab0804"
        "abracon,ab0805"
        "abracon,ab1801"
        "abracon,ab1803"
        "abracon,ab1804"
        "abracon,ab1805"
        "microcrystal,rv1805"
	Using "abracon,abx80x" will enable chip autodetection.
 - "reg": I2C bus address of the device

Optional properties:

The abx804 and abx805 have a trickle charger that is able to charge the
connected battery or supercap. Both the following properties have to be defined
and valid to enable charging:

 - "abracon,tc-diode": should be "standard" (0.6V) or "schottky" (0.3V)
 - "abracon,tc-resistor": should be <0>, <3>, <6> or <11>. 0 disables the output
                          resistor, the other values are in kOhm.
