Byteboi rev2 target

[abossard]

This pull request adds support for the CircuitMess ByteBoi Rev. 2 hardware target to the retro-go project. The changes introduce a new target configuration, including hardware pin mappings, display initialization, and build environment settings. Additionally, the SPI display driver is updated to allow target-specific SPI mode selection, and initialization routines are made more robust for shared SPI buses.

New hardware target: ByteBoi Rev. 2

• Added byteboi-rev2 target configuration file with all relevant hardware settings, pin mappings, display initialization sequence, and battery calculation macros in components/retro-go/targets/byteboi-rev2/config.h.
• Added documentation for ByteBoi Rev. 2, including hardware details, button mapping, display profile, flashing instructions, and verified app size examples in components/retro-go/targets/byteboi-rev2/docs/README.md.
• Added build environment configuration and default app set for ByteBoi Rev. 2 in components/retro-go/targets/byteboi-rev2/env.py.
• Added ESP-IDF sdkconfig file for ByteBoi Rev. 2, specifying serial flasher, optimization, SPI RAM, filesystem, and other settings in components/retro-go/targets/byteboi-rev2/sdkconfig.
• Enabled selection of ByteBoi Rev. 2 target in the main config header by including its config file when RG_TARGET_BYTEBOI_REV2 is defined in components/retro-go/config.h.

Display driver improvements

• Made SPI mode configurable per target by introducing RG_SCREEN_SPI_MODE macro and updating the SPI device interface config in components/retro-go/drivers/display/ili9341.h. [1] [2]
• Added logging of SPI display bus configuration for easier debugging in components/retro-go/drivers/display/ili9341.h.

Platform initialization robustness

• Improved SPI CS line initialization to check for valid GPIO numbers before setting direction and level, preventing issues with floating devices on shared buses in components/retro-go/rg_system.c.