Documentation: x86: convert usb-legacy-support.txt to reST

This converts the plain text documentation to reStructuredText format and
add 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: Jonathan Corbet <corbet@lwn.net>

Documentation/x86/index.rst

@@ -25,3 +25,4 @@ x86-specific Documentation
    pti
    microcode
    resctrl_ui
+   usb-legacy-support

Documentation/x86/usb-legacy-support.rst

@@ -1,7 +1,11 @@
-USB Legacy support
-~~~~~~~~~~~~~~~~~~
 
-Vojtech Pavlik <vojtech@suse.cz>, January 2004
+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+USB Legacy support
+==================
+
+:Author: Vojtech Pavlik <vojtech@suse.cz>, January 2004
 
 
 Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
@@ -27,18 +31,20 @@ It has several drawbacks, though:
 
 Solutions:
 
-Problem 1) can be solved by loading the USB drivers prior to loading the
-PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
-the kernel unconditionally, this means the USB drivers need to be
-compiled-in, too.
+Problem 1)
+  can be solved by loading the USB drivers prior to loading the
+  PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
+  the kernel unconditionally, this means the USB drivers need to be
+  compiled-in, too.
 
-Problem 2) can currently only be solved by either disabling HIGHMEM64G
-in the kernel config or USB Legacy support in the BIOS. A BIOS update
-could help, but so far no such update exists.
-
-Problem 3) is usually fixed by a BIOS update. Check the board
-manufacturers web site. If an update is not available, disable USB
-Legacy support in the BIOS. If this alone doesn't help, try also adding
-idle=poll on the kernel command line. The BIOS may be entering the SMM
-on the HLT instruction as well.
+Problem 2)
+  can currently only be solved by either disabling HIGHMEM64G
+  in the kernel config or USB Legacy support in the BIOS. A BIOS update
+  could help, but so far no such update exists.
 
+Problem 3)
+  is usually fixed by a BIOS update. Check the board
+  manufacturers web site. If an update is not available, disable USB
+  Legacy support in the BIOS. If this alone doesn't help, try also adding
+  idle=poll on the kernel command line. The BIOS may be entering the SMM
+  on the HLT instruction as well.