arm64: dts: s32g399a-rdb3: Enable the STM timers

arm64: dts: s32g399a-rdb3: Enable the STM timers

The platform has 8 CPUs, and the Linux STM timer driver is
instantiated per CPU.  Enable 8 STM timers that can be used as
replacements for the ARM architected timers.  The remaining STM timers
are not useful to the Linux kernel and provide no benefit, so they are
left disabled.

Enable STM0 to STM6 and STM8 on the s32g399a-rdb3 platform.

STM7 is skipped, as it differs slightly from the others and requires
an additional property to be properly handled by the driver.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Ghennadi Procopciuc <ghennadi.procopciuc@nxp.com>
Cc: Thomas Fossati <thomas.fossati@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>