powerpc: Remove dead BIO_VMERGE_BOUNDARY definition

The block layer dropped the virtual merge feature
(b8b3e16c).  BIO_VMERGE_BOUNDARY
definition is meaningless now (For POWER, BIO_VMERGE_BOUNDARY has been
meaningless for a long time since POWER disables the virtual merge
feature).
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/include/asm/io.h

@@ -713,13 +713,6 @@ static inline void * phys_to_virt(unsigned long address)
  */
 #define page_to_phys(page)	((phys_addr_t)page_to_pfn(page) << PAGE_SHIFT)
 
-/* We do NOT want virtual merging, it would put too much pressure on
- * our iommu allocator. Instead, we want drivers to be smart enough
- * to coalesce sglists that happen to have been mapped in a contiguous
- * way by the iommu
- */
-#define BIO_VMERGE_BOUNDARY	0
-
 /*
  * 32 bits still uses virt_to_bus() for it's implementation of DMA
  * mappings se we have to keep it defined here. We also have some old