ARC: Don't fiddle with non-existent caches

!CONFIG_ARC_HAS_(I|D)CACHE handles disabling caches from software,
mostly for debugging issues with new peripherals.
The scenario for non-existant caches, needs to be handled as well,
independnet of CONFIG_ARC_HAS_(I|D)CACHE

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Reported-by: Alexey Brodkin <abrodkin@synopsys.com>