pinctrl: intel: Add code name documentation

pinctrl: intel: Add code name documentation

Intel pinctrl drivers support large set of platforms and the IPs are
often reused by their different variants, but it's currently not possible
to figure out the exact driver that supports specific variant. Add user
friendly documentation for them.

Cc: stable@vger.kernel.org
Reported-by: Guido Trentalancia <guido@trentalancia.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220056
Signed-off-by: Raag Jadav <raag.jadav@intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Guido Trentalancia <guido@trentalancia.com>
[andy: added Oxford comma]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>