Change TMemCheck::Action to return whether to break rather than calling
PPCDebugInterface::BreakNow, as this simplified the implementation; then
remove said method, as that was its only caller.  One "interface" method
down, many to go...

- Move JitState::memcheck to JitOptions because it's an option.
- Add JitOptions::fastmem; switch JIT code to checking that rather than
  bFastmem directly.
- Add JitBase::UpdateMemoryOptions(), which sets both two JIT options
  (replacing the duplicate lines in Jit64 and JitIL that set memcheck
  from bMMU).
  - (!) The ARM JITs both had some lines that checked js.memcheck
    despite it being uninitialized in their cases.  I've added
    UpdateMemoryOptions to both.  There is a chance this could make
    something slower compared to the old behavior if the uninitialized
    value happened to be nonzero... hdkr should check this.
- UpdateMemoryOptions forces jo.fastmem and jo.memcheck off and on,
  respectively, if there are any watchpoints set.
- Also call that function from ClearCache.
- Have MemChecks call ClearCache when the {first,last} watchpoint is
  {added,removed}.

Enabling jo.memcheck (bah, confusing names) is currently pointless
because hitting a watchpoint does not interrupt the basic block.  That
will change in the next commit.

Various fixes to formatting and whitespace