[debug] add thread states for fs/gs registers

also delete previously introduced "extra regs" state

ZX-2258 # step 1

TESTED=None (these states are not used at the moment)

Change-Id: I80cf642b82187c209a0f43aeb10052d3ed87016f

[thread] clang-format on fs/gs register related files

ran zircon/scripts/clang-fmt on all the files I am about to edit

ZX-2258 # initial re-formatting

TESTED=None

Change-Id: Id963c5415469078558035c6f28ed39ceff3affce

[debugger] Add thread state for FP regs and FS/GS

Adds FPU, vector, and "extra" states to the CPU states that can be
queried and set via zx_thread_read/write_state.

ZX-2101

Change-Id: Ic809077a62d963bab578ee76379deb0c1e0362c1

[debugger] Set the single step flag in more places.

Previously the single step state would leak out of a thread and apply to
random threads on the system. This changes the single-step state from
being stored on the thread_t struct to always being stored in the
saved register context of the thread.

Change-Id: I72679c74ee6be4a77273e28463b3160f25daec5e

[debugger] Clarify thread state API

Firms up the contract for zx_read|write_thread_state and makes the state more
explicit for each platform.

The general register struct has been made for the current platform which
simplifies much fo the code.

The sizes are converted to size_t for consistency with other object calls.

Forwarding #defines and typedefs are included for downstream users until they
can be updated.

This will likely need to be revised somewhat again when we add more thread
states, which I plan to do in a followup.

Change-Id: I57e8e9979d073c8efdfaeb2683f9f83494d19abf

[kernel][status] Migrate the rest to zx_status_t

Change-Id: If0a5d3e04bfc3e2a57d068350ee1d1156ed67872

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[debugger] Remove 'priv' argument from arch_set_regset and up

This was always false, and in all implementations was ignored.

Change-Id: If23e701fe201a52f78b06f613799184250a83803

[kernel][debug] beginnings of register r/w support

This provides two syscalls mx_thread_read_state,mx_thread_write_state
that can be used to r/w cpu registers.
It is built off of the idea of "register sets" (integer, floating point,
and so on) in common use at least in gdb.

Discussion of the ultimate name of these syscalls, and whether to
merge them with something else is being left until the raft of
dependencies relying on this code is ready.

Change-Id: Ic118a76292334dfeaa46278aaddca3140ed4441c