[ARM] Feroceon: speed up flushing of the entire cache

Flushing the L1 D cache with a test/clean/invalidate loop is very
easy in software, but it is not the quickest way of doing it, as
there is a lot of overhead involved in re-scanning the cache from
the beginning every time we hit a dirty line.

This patch makes proc-feroceon.S use "clean+invalidate by set/way"
loops according to possible cache configuration of Feroceon CPUs
(either direct-mapped or 4-way set associative).

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>