power: axp818: Fix DCDC5 default voltage

DCDC5 is designed to supply VCC-DRAM, which is normally 1.5V for DDR3,
1.35V for DDR3L, and 1.2V for LPDDR3.

Also remove CONFIG_AXP_DCDC5_VOLT from h8_homlet_v2_defconfig.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>