microblaze: Improve ftrace time measuring

I had to comment sched_clock generic function because of broken toolchain.
It is fine grain timing.

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

arch/microblaze/include/asm/setup.h

@@ -28,8 +28,6 @@ void disable_early_printk(void);
 void heartbeat(void);
 void setup_heartbeat(void);
 
-unsigned long long sched_clock(void);
-
 #   ifdef CONFIG_MMU
 extern void mmu_reset(void);
 extern void early_console_reg_tlb_alloc(unsigned int addr);