microblaze: Enable SERIAL_OF_PLATFORM

SERIAL_OF_PLATFORM is required for getting 8250 to work.

Reported-by: Subbaraya Sundeep Bhatta <sbhatta@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/microblaze/configs/mmu_defconfig b/arch/microblaze/configs/mmu_defconfig
index deaf45a..e2f6543 100644
--- a/arch/microblaze/configs/mmu_defconfig
+++ b/arch/microblaze/configs/mmu_defconfig
@@ -49,6 +49,7 @@
 CONFIG_SERIAL_8250_CONSOLE=y
 CONFIG_SERIAL_UARTLITE=y
 CONFIG_SERIAL_UARTLITE_CONSOLE=y
+CONFIG_SERIAL_OF_PLATFORM=y
 # CONFIG_HW_RANDOM is not set
 CONFIG_XILINX_HWICAP=y
 CONFIG_I2C=y