microblaze: Select compilation flags via Kconfig

Remove autogenerated config.mk and select CPU options via Kconfig.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/microblaze-generic_defconfig b/configs/microblaze-generic_defconfig
index 8c7e4b7..7e53b5e 100644
--- a/configs/microblaze-generic_defconfig
+++ b/configs/microblaze-generic_defconfig
@@ -2,6 +2,9 @@
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_DM=y
 CONFIG_TARGET_MICROBLAZE_GENERIC=y
+CONFIG_XILINX_MICROBLAZE0_USE_BARREL=1
+CONFIG_XILINX_MICROBLAZE0_USE_DIV=1
+CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL=1
 CONFIG_SYS_TEXT_BASE=0x29000000
 CONFIG_DEFAULT_DEVICE_TREE="microblaze-generic"
 CONFIG_SPL=y