x86/io: Remove xlate_dev_kmem_ptr() duplication

Generic header defines xlate_dev_kmem_ptr().

Reuse it from generic header and remove in x86 code.
Move a description to the generic header as well.

Signed-off-by: Andy Shevchenko <[e-mail]>
Cc: Baolin Wang <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mika Westerberg <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/io.h

···
 #include <asm-generic/iomap.h>
 
 /*
- * Convert a virtual cached pointer to an uncached pointer
- */
-#define xlate_dev_kmem_ptr(p)	p
-
-/*
  * ISA space is 'always mapped' on a typical x86 system, no need to
  * explicitly ioremap() it. The fact that the ISA IO space is mapped
  * to PAGE_OFFSET is pure coincidence - it does not mean ISA values

include/asm-generic/io.h

···
 #endif /* CONFIG_GENERIC_IOMAP */
 #endif /* CONFIG_HAS_IOPORT_MAP */
 
+/*
+ * Convert a virtual cached pointer to an uncached pointer
+ */
 #ifndef xlate_dev_kmem_ptr
 #define xlate_dev_kmem_ptr xlate_dev_kmem_ptr
 static inline void *xlate_dev_kmem_ptr(void *addr)