Kbuild: Always use $(PHASE_)

It is confusing to have both "$(PHASE_)" and "$(XPL_)" be used in our
Makefiles as part of the macros to determine when to do something in our
Makefiles based on what phase of the build we are in. For consistency,
bring this down to a single macro and use "$(PHASE_)" only.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/doc/develop/tests_writing.rst b/doc/develop/tests_writing.rst
index 7ea1708..f6f852c 100644
--- a/doc/develop/tests_writing.rst
+++ b/doc/develop/tests_writing.rst
@@ -309,15 +309,15 @@
 Finally, add the test to the build by adding to the Makefile in the same
 directory::
 
-  obj-$(CONFIG_$(XPL_)CMDLINE) += wibble.o
+  obj-$(CONFIG_$(PHASE_)CMDLINE) += wibble.o
 
 Note that CMDLINE is never enabled in SPL, so this test will only be present in
 U-Boot proper. See below for how to do SPL tests.
 
 You can add an extra Kconfig check if needed::
 
-  ifneq ($(CONFIG_$(XPL_)WIBBLE),)
-  obj-$(CONFIG_$(XPL_)CMDLINE) += wibble.o
+  ifneq ($(CONFIG_$(PHASE_)WIBBLE),)
+  obj-$(CONFIG_$(PHASE_)CMDLINE) += wibble.o
   endif
 
 Each suite can have an optional init and uninit function. These are run before