[ARM] feroceon: remove CONFIG_CPU_DCACHE_WRITETHROUGH check

Since the Feroceon doesn't have a global WT override bit like
ARM926 does, remove all code relating to this mode of operation
from proc-feroceon.S.

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