ARC: mm: retire support for aliasing VIPT D$

Legacy ARC700 processors (first generation of MMU enabled ARC cores) had
VIPT cached which could be configured such that they could alias.
Corresponding support in kernel (with all the obnoxious cache flush overhead)
was added in ARC port 10 years ago to support 1 silicon. That is long bygone
and we can let it RIP.

Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>