Extend and rework the "Temporary Virtual Mappings" section of the
highmem.rst documentation.

Despite the local kmaps were introduced by Thomas Gleixner in October
2020, documentation was still missing information about them.  These
additions rely largely on Gleixner's patches, Jonathan Corbet's LWN
articles, comments by Ira Weiny and Matthew Wilcox, and in-code comments
from ./include/linux/highmem.h.

1) Add a paragraph to document kmap_local_page().
2) Reorder the list of functions by decreasing order of preference
   of use.
3) Rework part of the kmap() entry in list.

Link: https://lkml.kernel.org/r/20220428212455.892-5-fmdefrancesco@gmail.comSigned-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>