Remove all unused data types. Verified with a 'make allyesconfig'
and Cavium platform.

[paul.burton@mips.com:
  - Also checked via convoluted grep invocation for use of all removed
    structs & unions within arch/mips/ & drivers/.]
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/19711/
Cc: linux-mips@linux-mips.org
Cc: Chandrakala Chavva <cchavva@caviumnetworks.com>