extcon: arizona: Update manual headphone detection calculation

The higher levels of impedance have a higher minimum value than the
first level. As the same value was used for all levels, higher impedances
were reported with a very low level of accuracy. This patch applies the
approriate lower threshold for each level, whilst we are changing things
add a define for the maximum value at each level to improve readability.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>