Use partition with bootable flag as mmcpart

Signed-off-by: Daniel Abrecht <public@danielabrecht.ch>

configs/librem5_devkit_base_defconfig

@@ -73,3 +73,5 @@ CONFIG_USB_DWC3=y
 CONFIG_USB_DWC3_GADGET=y
 CONFIG_USB_XHCI_DWC3=y
 #CONFIG_DEBUG=y
+
+CONFIG_CMD_PART=y

configs/librem5_devkit_defconfig

@@ -76,3 +76,4 @@ CONFIG_USB_XHCI_DWC3=y
 
 CONFIG_M4_LOAD_DDR_TRAINING=y
 
+CONFIG_CMD_PART=y

include/configs/imx8m_som.h

@@ -170,7 +170,6 @@
 	"initrd_addr=0x43800000\0"		\
 	"initrd_high=0xffffffffffffffff\0" \
 	"mmcdev="__stringify(CONFIG_SYS_MMC_ENV_DEV)"\0" \
-	"mmcpart=" __stringify(CONFIG_SYS_MMC_IMG_LOAD_PART) "\0" \
 	"mmcroot=" CONFIG_MMCROOT " rootwait rw\0" \
 	"mmcautodetect=yes\0" \
 	"args_common=console=ttymxc0,115200 earlycon=ec_imx6q,0x30860000,115200 " \
@@ -181,11 +180,12 @@
 	"netargs=setenv bootargs ${bootargs} " \
                 "root=/dev/nfs nfsroot=${serverip}:${nfsroot},v3,tcp\0" \
 	"mmcargs=setenv bootargs ${bootargs} root=${mmcroot}\0 " \
-	"loadbootscript=ext2load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};\0" \
+	"findmmcpart=if itest.s \"x\" == \"x$mmcpart\"; then part list mmc ${mmcdev} -bootable mmcpart; fi\0" \
+	"loadbootscript=run findmmcpart; ext2load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};\0" \
 	"bootscript=echo Running bootscript from mmc ...; " \
 		"source\0" \
-	"loadimage=ext2load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}\0" \
-	"loadfdt=ext2load mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file}\0" \
+	"loadimage=run findmmcpart; ext2load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}\0" \
+	"loadfdt=run findmmcpart; ext2load mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file}\0" \
 	"rtos_file=imx8mq_m4_TCM_rpmsg_lite_str_echo_rtos.bin\0"       \
 	"rtos_bootaddr=0x7e0000\0"				       \
 	"rtosmmcboot=fatload mmc ${mmcdev}:${mmcpart} ${rtos_bootaddr} "  \