ARC: Cache: Move IOC initialization to a separate function

Move IOC initialization from cache_init() to a separate function.

This is the preparation for the next patch where we'll switch
to is_isa_arcv2() function usage instead of "CONFIG_ISA_ARCV2"
ifdef.

Also it makes cache_init function a bit cleaner.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>