imx: imx8ulp: enable MU0_B clk by default

Enable MU0_B clk by default. When M33 image is loaded by Jlink,
the previous method not enable MU0_B clk and not able to communicate
with M33, so let's enable it by default.

And we not put it under kernel dts, because it conflicts with i.MX8QM
suspend/resume logic which requires large change.

Reviewed-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8ulp/clock.c b/arch/arm/mach-imx/imx8ulp/clock.c
index 69cccaf..3e71a4f 100644
--- a/arch/arm/mach-imx/imx8ulp/clock.c
+++ b/arch/arm/mach-imx/imx8ulp/clock.c
@@ -214,6 +214,9 @@
 		pcc_reset_peripheral(4, SDHC2_PCC4_SLOT, false);
 	}
 
+	/* enable MU0_MUB clock before access the register of MU0_MUB */
+	pcc_clock_enable(3, MU0_B_PCC3_SLOT, true);
+
 	/*
 	 * Enable clock division
 	 * TODO: may not needed after ROM ready.