configs: convert CONFIG_SYS_MPUCLK to Kconfig

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/thuban_defconfig b/configs/thuban_defconfig
index a20c4df..dd61ead 100644
--- a/configs/thuban_defconfig
+++ b/configs/thuban_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_TARGET_THUBAN=y
+CONFIG_SYS_MPUCLK=300
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_LIBDISK_SUPPORT=y