For the parallel interface support the following changes were made:
1. Additional `lcd_*` pseudomodules are defined to control whether SPI serial or MCU 8080 8-/16-bit parallel interface is used.
2. The low level function implementation was extended for parallel interfaces so that the now can use either the SPI serial interface or the MCU 8080 8-/16-bit parallel interface.
Using the `lcc_*` modules, either the SPI serial interface or the MCU 8080 8-/16-bit interface or even both for multiple display can be used simultaneously.
In preparation for the parallel interface support the following changes were made:
1. The code for basic communication (acquire/release SPI device, SPI transfers), which were always implemented identically in the individual display drivers again and again, have been moved to the LCD driver as low-level functions and are now used by the display drivers. These low level function allow
- code deduplication on one hand and
- to define a more abstract communication interface on the other hand that can then be extended by parallel communication
2. Identical GPIO initialization has also been moved from display drivers to the LCD driver.
