Allow up to 2 KiB of arguments

Closes #161

Properly license all nontrivial files

Enable FPU in PK, regardless of FPU presence

Otherwise, the emulation code will refuse to emulate FP instructions.

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.

pk: does not use dtb

SBI: a0+a1 hold hartid+dtb pointer between boot loader stages

Allow PK access to user memory

WIP towards ECALL interface for SBI

Add ability to hard-code an initial environment

Add -p flag to pk to disable demand paging

when -s is passed, print time, instret, cycle, and CPI

Remove uarch counters

We'll re-add support for the generic performance counter facility once
it exists.

Move DRAM to high addresses

Don't assume existence of uarch counters

Refactor pk, bbl, machine into separate libraries

Yuck.

get rid of struct mainvars

Disentangle PK and BBL a bit

WIP on priv spec v1.9

Remove incorrect code supporting ELF32 on RV64 and vice-versa

This is technically possible by running an RV32 supervisor on an
RV64 machine, but the M-mode and S-mode code would need to be
compiled and linked separately.

Make boot loader/SBI changes to support SMP Linux

Split pk functionality into pk and bbl

pk is now an AEE only (i.e. it can only execute user programs).
bbl is now an SEE only (i.e. it can only host kernels).

new supervisor mode

Synced up PK with supervisor changes/asm syntax

You must upgrade to the latest compiler and ISA
simulator to build and run this version of the PK.

temporary undoing of renaming

Renamed packages

[pk] limit programs to 2GB (for RV32 simplicity)

[pk] load pk at addr 0; user stack top = MEMSIZE

[pk] add cache flush after program load

[sim,pk] reorganized status register

[xcc,pk,sim,opcodes] added first RVC instruction

[pk,fesvr] pk now loads elfs itself

this allows it to detect 32b binaries

[pk] send stdout/stderr to both fesvr and debug console

[opcodes, pk, sim, xcc] Tweaked FP encoding

[pk] various PK cleanups/speedups

[xcc, sim, pk] link register is now x1

[pk,sim,xcc] get rid of at register, introduce tp register

[pk] improved performance of fp emulation

[pk] zero out fp regs

[pk, sim] added FPU emulation support to proxy kernel

[pk] proxy kernel support for mixed 32b/64b operation

[pk,fesvr] improved proxykernel build system

Now uses a modified MCPPBS. Add --host=riscv to configure path.

Front-end server now just searches PATH for riscv-pk, so just install the pk
to somewhere in your path.