freescale/powerpc: Rename the config CONFIG_SECURE_BOOT name

Rename the CONFIG_SECURE_BOOT name to CONFIG_NXP_ESBC to avoid
conflicts with UEFI secure boot.

Signed-off-by: Udit Agarwal <udit.agarwal@nxp.com>
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig b/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig
index 7216412..e11757d 100644
--- a/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig
+++ b/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig
@@ -2,7 +2,7 @@
 CONFIG_SYS_TEXT_BASE=0x30001000
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
-CONFIG_SECURE_BOOT=y
+CONFIG_NXP_ESBC=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_DRIVERS_MISC_SUPPORT=y
 CONFIG_SPL=y