Update the dma clocks so that the magic numbers are named.

All the dma clocks have an enable bit to turn them on/off as
needed.  Currently these bits are in the code as "magic"
numbers.  This changes all of them to named defines to
improve code readability.

Also, the EP93XX_SYSCON_CLOCK_CONTROL register is improperly
named.  In the EP93xx User's Guide this register is called
PwrCnt (Power Control).  All of the uses of this register
are associated with the clock support so this patch also
modifies the names to match the User's Guide.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>