post: descend only when CONFIG_HAS_POST is defined

All objects under post/ directory are enabled by CONFIG_HAS_POST.
(post/tests.o is enabled by CONFIG_POST_STD_LIST.
But CONFIG_POST_STD_LIST depends on CONFIG_HAS_POST.)

We can move CONFIG_HAS_POST switch to the top Makefile.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/post/cpu/mpc83xx/Makefile b/post/cpu/mpc83xx/Makefile
index 4b3c50e..d57b667 100644
--- a/post/cpu/mpc83xx/Makefile
+++ b/post/cpu/mpc83xx/Makefile
@@ -5,4 +5,4 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_HAS_POST)	+= ecc.o
+obj-y += ecc.o
diff --git a/post/cpu/ppc4xx/Makefile b/post/cpu/ppc4xx/Makefile
index ed3e8e8..e9ec286 100644
--- a/post/cpu/ppc4xx/Makefile
+++ b/post/cpu/ppc4xx/Makefile
@@ -5,12 +5,12 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_HAS_POST)	+= cache_4xx.o
-obj-$(CONFIG_HAS_POST)	+= cache.o
-obj-$(CONFIG_HAS_POST)	+= denali_ecc.o
-obj-$(CONFIG_HAS_POST)	+= ether.o
-obj-$(CONFIG_HAS_POST)	+= fpu.o
-obj-$(CONFIG_HAS_POST)	+= ocm.o
-obj-$(CONFIG_HAS_POST)	+= spr.o
-obj-$(CONFIG_HAS_POST)	+= uart.o
-obj-$(CONFIG_HAS_POST)	+= watchdog.o
+obj-y += cache_4xx.o
+obj-y += cache.o
+obj-y += denali_ecc.o
+obj-y += ether.o
+obj-y += fpu.o
+obj-y += ocm.o
+obj-y += spr.o
+obj-y += uart.o
+obj-y += watchdog.o