Adds support for Northstar Plus (NS+) products to the PDC mailbox
driver.  The PDC driver was originally written to support the PDC
ring manager in the Northstar2 (64-bit) device.  The NS+ (32 bit
device) uses an almost identical ring manager, though with a
different name.  We just need to check for the type of hardware in
use, in order to write the appropriate interrupt configuration register.
Also updated DMA width to be correct for both NS+ and NS2.

Tested on NS+ and NS2.
Signed-off-by: Steve Lin <steven.lin1@broadcom.com>
Acked-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>