uboot-kirkwood: fix ethernet and usb

uboot-kirkwood: fix ethernet and usb

Before 2019.01 version was introduced patch, which changes cache
routines: 93b283d4 ("ARM: CPU: arm926ejs: Consolidate cache
routines to common file"). Unfortunately that patch make ethernet
and usb in kirkwood broken.

This patch backport commit 599f7aa5 ("ARM: kirkwood: disable dcache
for Kirkwood boards"), which are fix for that problem.

Fixes: dc08514e6d ("uboot-kirkwood: update to 2019.01")
Run tested: pogoplugv4

Tested-by: Cezary Jackiewicz <cezary@eko.one.pl> [nsa310]
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>