Convert CONFIG_SPL_LIBGENERIC_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/sunxi/Kconfig b/board/sunxi/Kconfig
index 94ba962..4534bb2 100644
--- a/board/sunxi/Kconfig
+++ b/board/sunxi/Kconfig
@@ -9,6 +9,9 @@
 config SPL_LIBDISK_SUPPORT
 	default y
 
+config SPL_LIBGENERIC_SUPPORT
+	default y
+
 # Note only one of these may be selected at a time! But hidden choices are
 # not supported by Kconfig
 config SUNXI_GEN_SUN4I
diff --git a/board/ti/common/Kconfig b/board/ti/common/Kconfig
index 604c687..8cae612 100644
--- a/board/ti/common/Kconfig
+++ b/board/ti/common/Kconfig
@@ -24,3 +24,6 @@
 
 config SPL_LIBDISK_SUPPORT
 	default y
+
+config SPL_LIBGENERIC_SUPPORT
+	default y