board: phytec: phycore_imx8mp: Add mcore support

Added m7 core support in uboot for imx8mp by adding
the boot variable prepare_mcore.

Based on commit 0ed32cc8568a ("LF-6555 imx8m[m/n/p/q]_evk: add
bootargs to support mcore")

Signed-off-by: Yashwanth Varakala <y.varakala@phytec.de>

board/phytec/phycore_imx8mp/phycore_imx8mp.env

@@ -30,7 +30,7 @@ ip_dyn=yes
 loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr_r} ${fdtfile}
 loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}
 mmcargs=
-	setenv bootargs console=${console}
+	setenv bootargs ${mcore_clk} console=${console}
 	root=/dev/mmcblk${mmcdev}p${mmcroot} ${raucargs} rootwait rw
 mmcautodetect=yes
 mmcboot=
@@ -51,7 +51,7 @@ mmcdev=CONFIG_SYS_MMC_ENV_DEV
 mmcpart=1
 mmcroot=2
 netargs=
-	setenv bootargs console=${console} root=/dev/nfs ip=dhcp
+	setenv bootargs ${mcore_clk} console=${console} root=/dev/nfs ip=dhcp
 	nfsroot=${serverip}:${nfsroot},v3,tcp
 netboot=
 	echo Booting from net ...;
@@ -74,4 +74,5 @@ netboot=
 		echo WARN: Cannot load the DT;
 	fi;
 nfsroot=/srv/nfs
+prepare_mcore=setenv mcore_clk clk-imx8mp.mcore_booted
 sd_dev=1