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/sama5d4ek_mmc_defconfig b/configs/sama5d4ek_mmc_defconfig
index 542ed66..ce9bc13 100644
--- a/configs/sama5d4ek_mmc_defconfig
+++ b/configs/sama5d4ek_mmc_defconfig
@@ -2,6 +2,7 @@
 CONFIG_ARCH_AT91=y
 CONFIG_TARGET_SAMA5D4EK=y
 CONFIG_SPL_GPIO_SUPPORT=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_FAT_SUPPORT=y
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4,SYS_USE_MMC"