First version chaining off SBI under QEMU

• PCI BAR size discovery (see Discover PCI BAR sizes #224)
• Memory range for PCI BARs discovery from FDT (needed to program BARs)
• PCI BAR allocation & programming (under QEMU BAR addresses start as zero)
• PCI device early setup (device programming needed)
• Linker script/toolchain/stubbed functionality
• MMIO UART
• Non-EFI loading support
• EFI support