rockchip: rk35xx-generic: Disable unused features

rockchip: rk35xx-generic: Disable unused features

The generic RK35xx board targets are intended to be used as a bare
minimum target that can be used to e.g. boot boards that mostly follow
reference hw design before a board spefic target has been added or for
flashing and recovery purposes.

Disable BOOTMETH_VBE, NET and ADC as these features are not intended to
ever be used by these minimal generic board targets.

Enable SYSRESET_PSCI to let TF-A handle sysreset from U-Boot proper.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>