powerpc/ftrace: Use CONFIG_FUNCTION_TRACER instead of CONFIG_DYNAMIC_FTRACE

Since commit 0c0c5230 ("powerpc: Only support DYNAMIC_FTRACE not
static"), CONFIG_DYNAMIC_FTRACE is always selected when
CONFIG_FUNCTION_TRACER is selected.

To avoid confusion and have the reader wonder what's happen when
CONFIG_FUNCTION_TRACER is selected and CONFIG_DYNAMIC_FTRACE is not,
use CONFIG_FUNCTION_TRACER in ifdefs instead of CONFIG_DYNAMIC_FTRACE.

As CONFIG_FUNCTION_GRAPH_TRACER depends on CONFIG_FUNCTION_TRACER,
ftrace.o doesn't need to appear for both symbols in Makefile.

Then as ftrace.o is built only when CONFIG_FUNCTION_TRACER is selected
ifdef CONFIG_FUNCTION_TRACER is not needed in ftrace.c, and since it
implies CONFIG_DYNAMIC_FTRACE, CONFIG_DYNAMIC_FTRACE is not needed
in ftrace.c
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/628d357503eb90b4a034f99b7df516caaff4d279.1652074503.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/trace/Makefile

@@ -14,9 +14,7 @@ obj64-$(CONFIG_FUNCTION_TRACER)		+= ftrace_mprofile.o
 else
 obj64-$(CONFIG_FUNCTION_TRACER)		+= ftrace_64_pg.o
 endif
-obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace_low.o
-obj-$(CONFIG_DYNAMIC_FTRACE)		+= ftrace.o
-obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o
+obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace_low.o ftrace.o
 obj-$(CONFIG_TRACING)			+= trace_clock.o
 
 obj-$(CONFIG_PPC64)			+= $(obj64-y)

arch/powerpc/kernel/trace/ftrace.c

@@ -28,9 +28,6 @@
 #include <asm/syscall.h>
 #include <asm/inst.h>
 
-
-#ifdef CONFIG_DYNAMIC_FTRACE
-
 /*
  * We generally only have a single long_branch tramp and at most 2 or 3 plt
  * tramps generated. But, we don't use the plt tramps currently. We also allot
@@ -783,7 +780,6 @@ int __init ftrace_dyn_arch_init(void)
 	return 0;
 }
 #endif
-#endif /* CONFIG_DYNAMIC_FTRACE */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER