Add ns16750 driver for ariane.

Temporary Workaround: Add hart filter check for sv32.

Properly license all nontrivial files

Fix problem of casting u64 to void* on 32-bit environment (#111)

Can't cast to pointer from 64 bit size integer directly on 32 bit
environment.

RISC-V: Support separate firmware and kernel payload

Support for separate firmware and kernel payload is added
by updating BBL to read optional preloaded kernel address
attributes from device-tree using a similar mechanism to
that used to pass init ramdisk addresses to linux kernel.

chosen {
riscv,kernel-start = <0x00000000 0x80200000>;
riscv,kernel-end = <0x00000000 0x80590634>;
};

These attributes are added by QEMU and read by BBL when combining
-bios <firmware-image> and -kernel <kernel-image> options. e.g.

$ qemu-system-riscv64 -machine virt -bios bbl -kernel vmlinux

With this change, bbl can be compiled without --with-payload
and the dummy payload alignment is altered to make the memory
footprint of the firmware-only bbl smaller. The dummy payload
message is updated to indicate the alternative load method.

This load method could also be supported by a first stage boot
loader that reads seperate firmware and kernel from SPI flash.
The main advantage of this new mechanism is that it eases kernel
development by avoiding the riscv-pk packaging step after kernel
builds, makes building per repository artefacts for CI simpler,
and mimics bootloaders on other platforms that can load a kernel
image file directly. Ultimately BBL should use an SPI driver to
load the kernel image however this mechanism supports use cases
such such as QEMU's -bios, -kernel and -initrd options following
examples from other platforms that pass kernel entry to firmware
via device-tree.

Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Alistair Francis <Alistair.Francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>

Detect harts that can't boot Linux instead of hard-coding them

This checks to see if a hart can't boot Linux by looking for a
compatible "mmu-type" field. If the hart can't boot Linux, then bbl
masks it off.

Add the '--enable-print-device-tree' argument

I'm trying to debug some device tree problems while booting Linux and
figured it would be really nice to have access to the device tree while
trying to debug these problems. I think this might be useful for lots
of people, so I went ahead and cleaned up the code enough that it should
actaully work in most cases.

Use uint64_t, not uintptr_t, to represent FDT addresses/sizes

This fixes RV32 pk.

Remove num_harts; use hart_mask exclusively

fdt: update the status length when masking cpus

fdt: redact clint, plic, and debug hardware

fdt: support redaction

clint: move hart wakeup till after all FDT parsing

The clint was wiping out information discovered by the plic.
Initialize hart stacks as they are discovered.
Then fill in clint+plic info
Then wake the harts.

fdt: look for the phandle of a cpu's nested interrupt controller

plic: discovered via fdt

fdt: rewrite parser using a single design pattern

fdt: add a size method

machine: add FDT parser