[ARM] 5310/1: Fix cache flush functions for ARMv4

ARMv4 (ARM720T) cache flush functions are broken in 2.6.19+ kernels.
The issue was introduced by commit f12d0d7c
This patch corrects the CPU_CP15 ifdef statements so that they actually
do something.

Signed-off-by: Anders Grafström <grfstrm@users.sourceforge.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>