drivers: mipi_dbi: stm32: fmc: add bank address property

The driver gets FMC bank address using
`FMC_BANK1_<parent_register_value>` define.

This approach has some flaws:
- The parent (bank) register's value might not correspond
  sequentially to the expected bank number.
  For example: `STM32_FMC_NOSRAM_BANK3` maps to `FMC_BANK1_4`,
  instead of `FMC_BANK1_3`.
- Some families don't even define the necessary `FMC_BANK1_x` macros.

To address this, the commit adds an optional `bank-address` property,
providing a direct way to define the FMC bank address for the driver.

Signed-off-by: Georgij Černyšiov <geo.cgv@gmail.com>