ARM: dts: rockchip: disable arm_global_timer on rk3066 and rk3188

The clock source and the sched_clock provided by the arm_global_timer
on Rockchip rk3066a/rk3188 are quite unstable because their rates
depend on the CPU frequency.

Recent changes to the arm_global_timer driver makes it impossible to use.

On the other side, the arm_global_timer has a higher rating than the
ROCKCHIP_TIMER, it will be selected by default by the time framework
while we want to use the stable Rockchip clock source.

Keep the arm_global_timer disabled in order to have the
DW_APB_TIMER (rk3066a) or ROCKCHIP_TIMER (rk3188) selected by default.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/f275ca8d-fd0a-26e5-b978-b7f3df815e0a@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>