Due to introducing the new peripheral clock handle functions,
use these functions to reduce duplicated code.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Tested-by: Heiko Schocher <hs@denx.de>
[Rebased on current master, fixup for at91rm9200ek]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>