ARM: STi: DT: STiH41x Add clk_ignore_unused to bootargs

Interconnect clocks are not yet managed at the init, then
we have to start the kernel with clk_ignore_unused.

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>