mfd: axp20x: Add a few missing defines for AXP288 specific registers

Add defines for the AXP288_POWER_REASON and AXP288_RT_BATT_V_H and
AXP288_RT_BATT_V_L and AXP288_BC_* registers. While at it also move the
AXP288_TS_ADC_H-AXP288_GP_ADC_L defines, which for some reason where
in a different place, together with the rest of the AXP288 specific
defines.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>