common: Drop CONFIG_HAS_POST

This only exists to control whether the post/ directory is build. It is
just as easy to check this in the Makefile. Remove CONFIG_HAS_POST and use
an ifdef in the Makefile instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index 3f332e6..9d7d8c2 100644
--- a/Makefile
+++ b/Makefile
@@ -763,7 +763,9 @@
 libs-y += common/
 libs-y += env/
 libs-$(CONFIG_API) += api/
-libs-$(CONFIG_HAS_POST) += post/
+ifdef CONFIG_POST
+libs-y += post/
+endif
 libs-$(CONFIG_UNIT_TEST) += test/ test/dm/
 libs-$(CONFIG_UT_ENV) += test/env/
 libs-$(CONFIG_UT_OPTEE) += test/optee/