meson8b: add the CPU_DIV16 clock for the ARM TWD

Carlo sent a .dts patch for the ARM TWD (timer watchdog) a long time
ago: [0]
This patch was never applied. While resurrecting it I found out (by trial and error) that the TWD clock is derived from the CPU clock by dividing the existing CPU clock by 16.
An additional hint was also given by Neil's clock measurer patch [1] as the GX SoCs explicitly define a "sys_cpu_div16" clock with ID 18, however old u-boot seems to call that CTS_LED_PLL_CLK. The rate of this clock also matches CPU clock divided by 16 on my boards.

It's not clear if there is an additional gate for this clock. If there is then it's not documented anywhere.

[0] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/391928.html
[1] https://patchwork.kernel.org/patch/10504083/

Martin Blumenstingl (2):
dt-bindings: clock: meson8b: export the CPU_DIV16 clock
clk: meson: meson8b: add the CPU_DIV16 clock

 drivers/clk/meson/meson8b.c              | 12 ++++++++++++
 drivers/clk/meson/meson8b.h              |  2 +-
 include/dt-bindings/clock/meson8b-clkc.h |  1 +
 3 files changed, 14 insertions(+), 1 deletion(-)