ttyFDC: Fix to use native endian MMIO reads

The MIPS Common Device Memory Map (CDMM) is internal to the core and has
native endianness. There is therefore no need to byte swap the accesses
on big endian targets, so convert the Fast Debug Channel (FDC) TTY
driver to use __raw_readl()/__raw_writel() rather than
ioread32()/iowrite32().

Fixes: 4cebec60 ("TTY: Add MIPS EJTAG Fast Debug Channel TTY driver")
Fixes: c2d7ef51

 ("ttyFDC: Implement KGDB IO operations.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9905/
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>