mfd: 88pm80x: Add 88pm860 chip type support

Add chip identification support for 88PM860 device
to the pm80x_chip_mapping table.

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>