Documentation: Fix typos

Fix typos in Documentation.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

ACPI: OSI: Update Documentation on custom _OSI strings

Originally, when there was some custom ASL needed for Linux, the
guidance for Linux-friendly OEMs was to introduced a new string in the
APCI tables and discuss it on the kernel mailing lists.

This lead to 3 strings being introduced. Those strings now have the
original problems fixed in the kernel and have since been removed.
The kernel no longer advertises any custom Linux-* _OSI strings for
OEM use.

It was discovered that these removed strings were actually being abused
to detect Linux for unrelated reasons, so drop the encouragement for
new ones to be added.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation: ACPI: Fix spelling mistake "Millenium" -> "Millennium"

There is a spelling mistake in the documentation with the Windows
Millennium edition. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation: ACPI: move osi.txt to firmware-guide/acpi and convert to reST

This converts the plain text documentation to reStructuredText format
and adds it to Sphinx TOC tree.

No essential content change.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>