ARC: Cache: Fix SLC operations when SLC is bypassed for data

If L1 D$ is disabled SLC is bypassed for data and all
load/store requests are sent directly to main memory.

If L1 I$ is disabled SLC is NOT bypassed for instructions
and all instruction requests are fetched through SLC.

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