mailbox: zynqmp: Move of_match structure closer to usage

The of_match structure zynqmp_ipi_of_match is now adjacent to where it
used in the zynqmp_ipi_driver structure for readability.

Signed-off-by: Ben Levinsky <ben.levinsky@amd.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>