MIPS: Standardize DTS files, status "ok" -> "okay"

MIPS: Standardize DTS files, status "ok" -> "okay"

While the current kernel code in drivers/of/ allows developers to be
sloppy and use the status value "ok", the current DTSpec 0.1 makes it
clear that the only officially proper spelling is "okay", so adjust
the very small number of DTS files under arch/mips/.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17227/
Signed-off-by: James Hogan <jhogan@kernel.org>