[ARM] nommu: rename compressed/head.S symbols to a new style

This patch renames symbols to a new style to prepare mpu support
code merging. e.g. __armv4_cache_on --> __armv4_mmu_cache_on

Signed-off-by: Hyok S. Choi <hyok.choi@samsung.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>