Requiring developers to calculate this pin-bit-value for each bank
is cumbersome and error-prone. With the routes-struct known in
the driver (see above and below), you can keep the the value element
in rockchip_pin_bank, but calculate the per-bank value dynamically
when the bank gets created.
For example in rockchip_pinctrl_get_soc_data just parse the route-struct
and calculate that value when the driver probes.
This reduces possible errors and also spares us the clutter of all the
additional PIN_BANK_* defines.