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>

diff --cc arch/microblaze/kernel/Makefile
Simple merge

diff --cc arch/microblaze/kernel/ftrace.c
Simple merge

diff --cc arch/microblaze/lib/Makefile
Simple merge