edma: simplify 64-bit support

Move all 64-bit handling into defines rather than having them split all
over the code. The SET_CH_64/writeq_ch() are implemented as two 32-bit
writes rather than a call to writeq as the respective field is not
aligned, thus accessing it with writeq generates alignement exception.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
[vzapolskiy: removed SET_CH_64() macro]
Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>