usb: xhci: improve xhci-caps.h comments

usb: xhci: improve xhci-caps.h comments

No functional changes.

This patch updates comments in xhci-caps.h for better readability and
consistency. Each Capability Register bit field now includes a brief
description of its name and valid range, following a uniform comment
format across the file.

These updates are based on the xHCI specification, revision 1.2.

Bit field comment format:
/* <bit range> - <Field name>,<noteworthy information if any> */

Why print the bit range?
 The bit range aids in identifying missing macros and reserved bit ranges.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20251119142417.2820519-19-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>