fsl-viu: cleanup clock API use

use devm_clk_get() for automatic put after device close, check for and
propagate errors when enabling clocks, need to prepare clocks before
they can get enabled, adjust code paths to correctly balance get/put and
prepare/unprepare and enable/disable calls

Cc: Mauro Carvalho Chehab <m.chehab@samsung.com>
Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>