MIPS: Remove TX39XX support

No (active) developer owns this hardware, so let's remove Linux support.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>

MIPS/IRQCHIP: Move irq_chip from arch/mips to drivers/irqchip.

While at it, rename it because in drivers/irqchip no longer every CPU is
a MIPS.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

MIPS: Move headfiles to new location below arch/mips/include

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>