65c816: assorted low level fixes

65c816: assorted low level fixes

With these fixed we get to a shell prompt and can run some commands. To get
further is going to need cc65 modifications as cc65 generates the following
code in /bin/ls

	STA $08			3
	STX $09			3
	JMP $0008		5

which of course goes castors up on the 65C816 set up because DP is not B:0000
nor can it be.

So far this seems to be the only problem case and it looks as if generating a

	PHX			3
	PHA			3
	RTS			6

would be within one clock for 65C02 or later. 6502 compatible code
will need an uglier fixup I fear.

	STA $08			3
	TXA			2
	PHA			3
	LDA $08			3
	PHA			3
	RTS			6

or similar which isn't pretty but works (self modifying code isn't on
because we might re-enter mid execution)