clk: meson-gxbb: Add EE 32K Clock for CEC

On Amlogic GX SoCs, there is two CEC controllers :
- An Amlogic CEC custom in the AO domain
- The Synopsys HDMI-TX Controller in the EE domain

Each of these controllers needs a 32.768KHz clock, but there is two paths :
- In the EE domain, the "32k_clk" this patchs is adding
- In the AO domain, with a more complex dual divider more precise setup

The AO 32K clock support will be pushed later in the corresponding
gxbb-aoclk driver when the AE CEC driver is ready.

The EE 32k_clk must be pushed earlier since mainline support for CEC in the
Synopsys HDMI-TX controller is nearby.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
[Rebased patch on top of last changes]
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>