api: Convert to Kconfig

Now that we have a Kconfig for the API, convert the two boards that
are using this to Kconfig and remove CONFIG_API from the whitelist.

Signed-off-by: Emmanuel Vadot <manu@bidouilliste.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/PMC440_defconfig b/configs/PMC440_defconfig
index 0bcc586..7380ba7 100644
--- a/configs/PMC440_defconfig
+++ b/configs/PMC440_defconfig
@@ -24,3 +24,4 @@
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_OF_LIBFDT=y
+CONFIG_API=y