Pico_Plus_2: cleanup pin-names

[bablokb]

This PR does some cleanup on pin-names:

• renamed SPICE_xxx to SPCE_xxx (Pimoroni calls their connector SP/CE)
• removed SPI (board.SPI() throws NotImplementedError anyways)
• added normal GPxx names since all pins are normal GPIOs as well
• removed SPICE_TX and SPICE_RX. RX/TX pin names are UART-related on other boards. Here, they are only inclusive names for MOSI/MISO. It turns out that SPICE_TX is an UART-RX and vice versa. So to avoid confusion, I removed the names.

Adding a board_spi_obj (thus preventing the NotImplementedError) would be possible, but I don't think this makes sense. The SP/CE connector lacks a DC-pin and busy-pin. So to drive a SPI-screen, it is better to create an SPI object without MISO and use the pin for DC.

I would even suggest to remove SCK, MISO and MOSI as well. They are already defined as SPCE_SCK (and so on). The pure names suggest that there is something like a default SCK/MISO/MOSI on the Pico, which is not the case and is not implemented for other Pico-boards.

@ZodiusInfuser: maybe you could chime in and share your opinion regarding the pin-names

[ZodiusInfuser]

I believe the SPICE name was copied from what @Gadgetoid set within our C header for the product (e.g. https://github.com/pimoroni/pimoroni-pico-rp2350/blob/feature/wireless/micropython/board/PIMORONI_PICO_PLUS2/pimoroni_pico_plus2w_rp2350.h), though why he included the I I don't know.

The other changes sound sensible to me.

[Gadgetoid]

"SPICE" flows better and is easier to say, I will die on this hill.

[dhalbert]

Whatever is consistent for your pin names elsewhere (MicroPython, Arduino, board silk, etc.) is OK with us. The pin can have multiple names if that would be helpful.

[bablokb]

Although I use SPICE for simulation and when I am cooking, I have no problem reverting to SPICE naming again to make all spice boys and girls happy. Just let me know.