Adding Framebuffer, SD card and PCIe support to the Raspberry Pi 4b BSP

This project extends the Raspberry Pi 4b BSP in RTMES by adding Framebuffer, SDHCI and PCIe support. Building on mailbox and DMA support added during GSoC 2025, this project completes the SDHCI work pending since GSoC 2024 and adds framebuffer otuput via the VideoCore mailbox property tags interface. PCIe support will be ported to rtems-libbsd. In this proposal I have detailed how I will go about adding support and testing each driver.