mfd: qcom-spmi-pmic: Add support for PM660/PM660L

Add the subtype and compatible strings for PM660 and PM660L,
found in various SoCs, including SDM630, SDM636, SDM660 and
SDA variants.

Signed-off-by: AngeloGioacchino Del Regno <kholk11@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>