[IA64] remove dead BIO_VMERGE_BOUNDARY definition

The block layer dropped the virtual merge feature
(b8b3e16c). BIO_VMERGE_BOUNDARY
definition is meaningless now (For IA64, BIO_VMERGE_BOUNDARY has been
meaningless for a long time since IA64 disables the virtual merge
feature).
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/include/asm/io.h

@@ -434,28 +434,4 @@ extern void memset_io(volatile void __iomem *s, int c, long n);
 
 # endif /* __KERNEL__ */
 
-/*
- * Enabling BIO_VMERGE_BOUNDARY forces us to turn off I/O MMU bypassing.  It is said that
- * BIO-level virtual merging can give up to 4% performance boost (not verified for ia64).
- * On the other hand, we know that I/O MMU bypassing gives ~8% performance improvement on
- * SPECweb-like workloads on zx1-based machines.  Thus, for now we favor I/O MMU bypassing
- * over BIO-level virtual merging.
- */
-extern unsigned long ia64_max_iommu_merge_mask;
-#if 1
-#define BIO_VMERGE_BOUNDARY	0
-#else
-/*
- * It makes no sense at all to have this BIO_VMERGE_BOUNDARY macro here.  Should be
- * replaced by dma_merge_mask() or something of that sort.  Note: the only way
- * BIO_VMERGE_BOUNDARY is used is to mask off bits.  Effectively, our definition gets
- * expanded into:
- *
- *	addr & ((ia64_max_iommu_merge_mask + 1) - 1) == (addr & ia64_max_iommu_vmerge_mask)
- *
- * which is precisely what we want.
- */
-#define BIO_VMERGE_BOUNDARY	(ia64_max_iommu_merge_mask + 1)
-#endif
-
 #endif /* _ASM_IA64_IO_H */