The code is rather based on trial-and-error than knowledge. Verified Via
Rhine functionality in PIO as well as MMIO mode.

[Looks sane -- Ralf]
Signed-off-by: NPhil Sutter <n0-1@freewrt.org>
Tested-by: NFlorian Fainelli <florian@openwrt.org>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>