The legacy Allwinner ATF port used to setup some clocks, and U-Boot is
still relying on this. We don't need to setup the full set, as the SPL
is doing most of it, but it misses one clock (AHB2) and programs another
(AHB1) to quite conservative values.

Fix this up during the platform setup to improve USB and Ethernet
performance, iperf values go up by 31% in my setup with that patch.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>