clk: meson: meson8b: Drop CLK_IS_CRITICAL from fclk_div2

Drop CLK_IS_CRITICAL from fclk_div2. This was added because we didn't
know the relation between this clock and RGMII Ethernet. It turns out
that fclk_div2 is used as "timing adjustment clock" to generate the RX
delay on the MAC side - which was enabled by u-boot on Odriod-C1. When
using the RX delay on the PHY side or not using a RX delay at all then
this clock can be disabled.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200620161422.24114-1-martin.blumenstingl@googlemail.com