ARCv2: smp-boot: wake_flag polling by non-Masters needs to be uncached

This is needed on HS38 cores, for setting up IO-Coherency aperture properly

The polling could perturb the caches and coherecy fabric which could be
wrong in the small window when Master is setting up IOC aperture etc
in arc_cache_init()

We do it only for ARCv2 based builds to not affect EZChip ARCompact
based platform.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>