MIPS: Octeon: Remove extern declarations.

Get rid of extern declarations in .c functions and included
the necessary header file. Also remove unused UART declares.

Signed-off-by: Steven J. Hill <steven.hill@cavium.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/19477/
Cc: linux-mips@linux-mips.org