memory: brcmstb: dpfe: use msleep() over udelay()

To be more "scheduler friendly", we use msleep() rather than udelay()
while we wait for the DCPU to respond.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>