docs: fix pointers to io-mapping.rst and io_ordering.rst files

Those files got moved, but cross-references still point to the
wrong places.

Fixes: fcd680727157 ("Documentation: Add io-mapping.rst to driver-api manual")
Fixes: d1ce350015d8 ("Documentation: Add io_ordering.rst to driver-api manual")
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Reviewed-by: Alex Shi <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/c02051[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/PCI/pci.rst

···
 as the PCI "bus address" might have been remapped to a "host physical"
 address by the arch/chip-set specific kernel support.
 
-See Documentation/io-mapping.txt for how to access device registers
+See Documentation/driver-api/io-mapping.rst for how to access device registers
 or device memory.
 
 The device driver needs to call pci_request_region() to verify

Documentation/translations/zh_CN/io_ordering.txt

···
-Chinese translated version of Documentation/io_ordering.txt
+Chinese translated version of Documentation/driver-api/io_ordering.rst
 
 If you have any comment or update to the content, please contact the
 original document maintainer directly.  However, if you have a problem
···
 
 Chinese maintainer: Lin Yongting <[e-mail]>
 ---------------------------------------------------------------------
-Documentation/io_ordering.txt 的中文翻译
+Documentation/driver-api/io_ordering.rst 的中文翻译
 
 如果想评论或更新本文的内容，请直接联系原文档的维护者。如果你使用英文
 交流有困难的话，也可以向中文版维护者求助。如果本翻译更新不及时或者翻

arch/unicore32/include/asm/io.h

···
  * ioremap and friends.
  *
  * ioremap takes a PCI memory address, as specified in
- * Documentation/io-mapping.txt.
+ * Documentation/driver-api/io-mapping.rst.
  *
  */
 #define ioremap(cookie, size)		__uc32_ioremap(cookie, size)

include/linux/io-mapping.h

···
  * The io_mapping mechanism provides an abstraction for mapping
  * individual pages from an io device to the CPU in an efficient fashion.
  *
- * See Documentation/io-mapping.txt
+ * See Documentation/driver-api/io-mapping.rst
  */
 
 struct io_mapping {