Input: synaptics - enable InterTouch on Dell Inspiron 3521

The Synaptics touchpad on Dell Inspiron 3521 (PNP ID DLL0597) advertises
InterTouch / SMBus support, but is not on the SMBus passlist, so the
driver falls back to PS/2 and logs a hint to try
psmouse.synaptics_intertouch=1.

Add DLL0597 to smbus_pnp_ids so InterTouch is enabled automatically on
this model (and other Dells that reuse the same PNP ID).

Hardware: Dell Inc. Inspiron 3521 (board 06RYX8, BIOS A07),
Synaptics fw 8.1 / board id 2382, firmware_id "PNP: DLL0597 PNP0f13".

Signed-off-by: Shashwat Agrawal <shashwatagrawal473@gmail.com>
Link: https://patch.msgid.link/20260626130051.2574-1-shashwatagrawal473@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>