Convert CONFIG_SPL_LIBCOMMON_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/microblaze-generic_defconfig b/configs/microblaze-generic_defconfig
index 047fd60..19f0343 100644
--- a/configs/microblaze-generic_defconfig
+++ b/configs/microblaze-generic_defconfig
@@ -1,4 +1,5 @@
 CONFIG_MICROBLAZE=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_TARGET_MICROBLAZE_GENERIC=y
 CONFIG_XILINX_MICROBLAZE0_USE_MSR_INSTR=1
 CONFIG_XILINX_MICROBLAZE0_USE_BARREL=1