Documentation/protection-keys: Clean up documentation for User Space pkeys

The documentation for user space pkeys was a bit dated including things
such as Amazon and distribution testing information which is irrelevant
now.

Update the documentation. This also streamlines adding the Supervisor
pkey documentation later on.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20220419170649.1022246-2-ira.weiny@intel.com

x86/Kconfig: Update config and kernel doc for MPK feature on AMD

AMD's next generation of EPYC processors support the MPK (Memory
Protection Keys) feature. Update the dependency and documentation.

Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/159068199556.26992.17733929401377275140.stgit@naples-babu.amd.com

docs: move protection-keys.rst to the core-api book

This document is used by multiple architectures:

$ echo $(git grep -l pkey_mprotect arch|cut -d'/' -f 2|sort|uniq)
alpha arm arm64 ia64 m68k microblaze mips parisc powerpc s390 sh sparc x86 xtensa

So, let's move it to the core book and adjust the links to it
accordingly.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>