WIP towards ECALL interface for SBI

Cleanly separate HTIF code; don't poll keyboard on timer interrupt

zero-extend RV32 physical addresses for HTIF

Disentangle PK and BBL a bit

Remove SBI HTIF support; add console_getchar

Fix struct stat size mismatch for RV32

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).

Merge [shm]call into ecall, [shm]ret into eret

Use hcall instead of mcall for sbi calls

Update to new privileged spec

Support linkat, unlinkat, mkdirat syscalls

Also, old-style syscalls e.g. open are now implemented with e.g. openat.

Turn off interrupts when talking to host

Add several syscalls, and move syscall header file from newlib
syscalls added (openat, access, accessat, faccessat, etc.)

Abandon MIPS convention for indicating syscall errors in register a3

Update to new privileged ISA

add BSD license

fix spinlocks; add --disable-atomics cfg opt

new tohost/fromhost semantics

temporary undoing of renaming

Renamed packages

[sim,pk] cleanups & initial virtual memory support

[pk] add cache flush after program load

[xcc,pk,sim] added privileged cflush instruction

[xcc,pk,opcodes,sim] updated encoding/insn names

[pk] no amos for now, add a sync before triggering the frontend

[sim, xcc] added PCRs to replace k0 and k1

[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.