MLK-19355 imx8mm: Enable sec_debug clock in SPL

ipg_stop from GPC is not connected to WDOG directly, the sec_debug clock is
used to sample the ipg_stop from GPC. So when this clock is off, ipg_stop input
of WDOG can’t assert, WDOG will fail to stop in DSM mode.
Enable this clock forever in SPL, so other SW don't need to touch it.
Signed-off-by: Ye Li <ye.li@nxp.com>
Tested-by: Bai Ping <ping.bai@nxp.com>
(cherry picked from commit 1da6c9b3a837d15c25086af449462d5e8b56c290)

arch/arm/cpu/armv8/imx8m/clock_imx8mm.c

@@ -717,6 +717,8 @@ int clock_init()
 	clock_enable(CCGR_ECSPI2, 1);
 	clock_enable(CCGR_ECSPI3, 1);
 
+	clock_enable(CCGR_SEC_DEBUG, 1);
+
 	enable_display_clk(1);
 	return 0;
 };