sh: Account for cache aliases in flush_icache_range()

The icache may also contain aliases so we must account for them just
like we do when manipulating the dcache. We usually get away with
aliases in the icache because the instructions that are read from memory
are read-only, i.e. they never change. However, the place where this
bites us is when the code has been modified.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>