On the Khadas VIM2 (GXM) and LePotato (GXL) board there are problems
with reboot; e.g. a ~60 second delay between issuing reboot and the
board power cycling (and in some OS configurations reboot will fail
and require manual power cycling).

Similar to 'commit c987ac6f ("clk:
meson-gxbb: set fclk_div2 as CLK_IS_CRITICAL")' the SCPI Cortex-M4
Co-Processor seems to depend on FCLK_DIV3 being operational.

Until commit 05f81440 ("clk:
meson: add fdiv clock gates"), this clock was modeled and left on by
the bootloader.

We don't have precise documentation about the SCPI Co-Processor and
its clock requirement so we are learning things the hard way.

Marking this clock as critical solves the problem but it should not
be viewed as final solution. Ideally, the SCPI driver should claim
these clocks. We also depends on some clock hand-off mechanism
making its way to CCF, to make sure the clock stays on between its
registration and the SCPI driver probe.

Fixes: 05f81440 ("clk: meson: add fdiv clock gates")
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>