rockchip: rk3399: remove duplicate call to regulators_enable_boot_on

rockchip: rk3399: remove duplicate call to regulators_enable_boot_on

An earlier commit makes the common SPL code call
regulators_enable_boot_on and regulators_enable_boot_off before
iterating over possible boot media for U-Boot proper. There is therefore
no need to do this in the rk3399-specific code, so let's remove it.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Tested-by: Xavier Drudis Ferran <xdrudis@tinet.cat>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>