mailbox: zynqmp: ipi mailbox driver

ZynqMP mailbox driver implementing IPI communication with PMU. This would
allow U-Boot SPL to communicate with PMUFW to request privileged
operations.

Signed-off-by: Ibai Erkiaga <ibai.erkiaga-elorza@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 59c766f..6af9816 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -449,6 +449,7 @@
 F:	drivers/i2c/i2c-cdns.c
 F:	drivers/i2c/muxes/pca954x.c
 F:	drivers/i2c/zynq_i2c.c
+F:	drivers/mailbox/zynqmp-ipi.c
 F:	drivers/mmc/zynq_sdhci.c
 F:	drivers/mtd/nand/raw/zynq_nand.c
 F:	drivers/net/phy/xilinx_phy.c