blackfin: Add more dcache functions

Add invalidate_dcache_range() and flush_dcache_range() for the blackfin
architecture. Such functions already exist on this arch with different
names, so just forward the call.

This fixes the build of bf609-ezkit board as it uses
drivers/net/designware.c which requires the above functions.

Cc: Sonic Zhang <sonic.adi@gmail.com>, Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vasili Galka <vvv444@gmail.com>