clk: imx6sx: remove clks_init_on array

Clock framework will enable those clocks registered
with CLK_IS_CRITICAL flag, so no need to have
clks_init_on array during clock initialization now.

ARM clock is busy divider type which has the
CLK_IS_CRITICAL flag set by default when registered.

IPG clock has no clock gate and its parent AHB clock
is busy divider type, so no need to add CLK_IS_CRITICAL
flag for IPG clock.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>