regulator: rk8xx: fix SWITCH enable on RK809

On RK809 in PMIC_POWER_ENX registers, in order to set or clear a bit N,
the bit at offset N + 4 needs to be set otherwise nothing is done.

This fixes the inability to modify the SWITCH state on RK809.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: William Wu <william.wu@rock-chips.com>
[reworded commit log]
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>