mfd: simple-mfd-i2c: Add Delta TN48M CPLD support

mfd: simple-mfd-i2c: Add Delta TN48M CPLD support

Delta TN48M switches have a Lattice CPLD that serves
multiple purposes including being a GPIO expander.

So, lets use the simple I2C MFD driver to provide the MFD core.

Also add a virtual symbol which pulls in the simple-mfd-i2c driver and
provide a common symbol on which the subdevice drivers can depend on.

Fixes: b3dcb5de6209 ("gpio: Add Delta TN48M CPLD GPIO driver")
Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Link: https://lore.kernel.org/20220131133049.77780-2-robert.marko@sartura.hr
Link: https://lore.kernel.org/linux-gpio/20260112064950.3837737-1-rdunlap@infradead.org/
Signed-off-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260112-mfd-tn48m-v11-1-00c798d8cd2a@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>