ARM: l2c: clean up OF initialisation a bit

Rather than having a boolean and other tricks to disable some bits of
l2x0_init(), split this function into two parts: a common part shared
between OF and non-OF, and the non-OF part.

The common part can take a block of function pointers, and the cache
ID (to cope with Aurora's DT specified ID.)  Eliminate the redundant
setting of l2x0_base in the OF case, moving it to the non-OF init
function.

This allows us to localise the OF-specific initialisation handling
from the non-OF handling.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>