As M4 is sourcing UART clk from OSC, to make UART work when M4 is enabled, need to select OSC as clk parent, 24M OSC is enough for debug UART in uboot. Signed-off-by: Peng Fan <peng.fan@nxp.com> Cc: Stefano Babic <sbabic@denx.de> Cc: Fabio Estevam <fabio.estevam@nxp.com>