ENGR00315894-76 mx6 clock: Add vadc clock enable function

ENGR00315894-76 mx6 clock: Add vadc clock enable function

Add vadc clock enable function.

Signed-off-by: Sandor Yu <R01008@freescale.com>
Signed-off-by: Ye.Li <B37916@freescale.com>
(cherry picked from commit 721c7a1448c5b7265b597b83d18f8338a27ea213)
Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
(cherry picked from commit 903a59ef941f39b6d7f693dd7c60528e166de079)
(cherry picked from commit dc767fb7d5c155f2a6ef01c4dee808b9c1944fc2)
(cherry picked from commit 0a48932f375a969e6f7e72d171522146981b2135)
(cherry picked from commit b6f962db57c988c31d35e204f638ba3b0c53eb4a)