staging: fsl-mc: use 32bits to support 64K size mc-portals

As per APIs each mc-portal is of 64K size while currently
16bits (type u16) is used to store size of mc-portal.
In these cases upper bit of portal size gets truncated.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@nxp.com>
Acked-By: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>