csky: Add setup_initrd check code

We should give some necessary check for initrd just like other
architectures and it seems that setup_initrd() could be a common
code for all architectures.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/kernel/setup.c

@@ -47,9 +47,6 @@ static void __init csky_memblock_init(void)
 	signed long size;
 
 	memblock_reserve(__pa(_stext), _end - _stext);
-#ifdef CONFIG_BLK_DEV_INITRD
-	memblock_reserve(__pa(initrd_start), initrd_end - initrd_start);
-#endif
 
 	early_init_fdt_reserve_self();
 	early_init_fdt_scan_reserved_mem();