microblaze: Fix ftrace

- Do not trace idle loop which takes a lot time
- Fix cache handling in generic ftrace code
- Do not trace lib functions ashldi3, ashrdi3, lshrdi3
  Functions are called from generic ftrace code which
  can't be traced

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/lib/Makefile

@@ -2,6 +2,12 @@
 # Makefile
 #
 
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_ashldi3.o = -pg
+CFLAGS_REMOVE_ashrdi3.o = -pg
+CFLAGS_REMOVE_lshrdi3.o = -pg
+endif
+
 lib-y :=  memset.o
 
 ifeq ($(CONFIG_OPT_LIB_ASM),y)