Debian toolchain defaults to PIE, and I guess that will also be the case
of most distributions. This cause bbl to be non-functional.

This patch fixes that by adding -fno-PIE in the default CFLAGS.

Reboot does not work reliably without this.

* Changed install_subdir to $host_alias with substituted 64->32 instead of hardcoded riscv[32|64]-unknown-elf

* Updated readme to reflect changes in install_subdir.

Closes #87

Closes #88

Otherwise, linux complains the moment an interrupt arrives and
wakes up one of the not-looping cores.

This makes it more compatible with recent glibc.

mtrap: loop forever, really

gcc sometimes takes liberties with optimizing away our important halt function!

Boot on the first hart

This code is broken, and it's left over from before we could read the
DTB to find harts to boot on.

Add __riscv_flush_icache

For BBL's purposes a local i-cache flush should be sufficient.

Add a 16550 UART driver to back the SBI console

QEMU currently provides the console via HTIF and the SBI.  That's a bit
messy because BBL polls for serial input, which means that typing too
quickly loses characters.  While QEMU has a standard 16550 device model,
there's no way to have two consoles share the console in QEMU (as they'd
step all over each other) so that means we can't have both the HTIF
console and the 16550 console.

With this patch, QEMU can be changed to use a 16650 instead of the HTIF
for serial output.  Linux will use the SBI for early printk support
(which is fine, polling for output is stable) and then swap over as soon
as it detects the UART.  When Linux swaps it prints out the whole
history, but there's probably a way to get around that.  There's a few
lines that are output to both, but it appears the Linux driver is close
enough to ours that nothing catastrophic happens -- there's not much to
the device, so hopefully that pans out on real hardware too.

Once Linux swaps over to natively using the driver we get reliable
console input.  If you don't have the in-kernel driver then Linux never
swaps over and keeps using the SBI console just like before.

Fix line endings in the logo

Remove the platform interface

We now automatically detect everything that the platform interface used
to be used for, so it's now obsolete!

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

Without this I can't get printf to show me debug info during early boot.

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.

Per the Unix-class platform spec

The DTB argument to boot_other_hart shouldn't be used in BBL

I screwed up refactoring bbl.

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.

Add a platform interface