i.MX6: provide functional names for CCM_CCGR0-CCGR6 bit fields

Add meaningful constants for each clock channels and use them for
enabling and disabling i.MX6 clocks.

Includes an update to enable/disable the IPU1 clock in
drivers/video/ipu_common to remove IMX5x register access
when used on i.MX6 as discussed in V1:

     http://patchwork.ozlabs.org/patch/185129/



Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>