soc: microchip: mpfs: use a consistent completion timeout

Completion timeouts use jiffies, so passing a number directly will
produce inconsistent timeouts depending on config. Define the timeout in
ms and convert it to jiffies instead.

Tested-by: Valentina Fernandez <valentina.fernandezalanis@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>