mfd: arizona: Add TST_CAP bits for headphone detection

On wm5110/8280 some additional settings are required to get accurate
measurements at the top end of the headphone detection range. This patch
adds the bits required for this.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>