Add basic support for running directly on top of SBI, with no UEFI
firmware present. Build as e.g.:
make CROSS=riscv64-linux-gnu- bin-riscv64/ipxe.sbi
The resulting binary can be tested in QEMU using e.g.:
qemu-system-riscv64 -M virt -cpu max -serial stdio \
-kernel bin-riscv64/ipxe.sbi
No drivers or executable binary formats are supported yet, but the
unit test suite may be run successfully.
Signed-off-by: Michael Brown <mcb30@ipxe.org>