dma: mmp_pdma: factor out DRCMR register calculation

The exact same calculation is done twice, so let's factor it out to a
macro.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>