MIPS: octeon: Get rid of preprocessor directives around RESERVE32

Some of them were pointless because CONFIG_CAVIUM_RESERVE32 is now always
defined, some were not enough (Yu Zhao reported
"Failed to allocate CAVIUM_RESERVE32 memory area" error).

Removing the directives allows for compiler coverage of RESERVE32 code and
replacing one of [always-true] "ifdef" with a compiler conditional fixes
the [cosmetic] error message.

Fixes: 3e3114ac ("MIPS: Introduce CAVIUM_RESERVE32 Kconfig option")

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>