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/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
index a753cc4..d2ace8c 100644
--- a/drivers/mailbox/Makefile
+++ b/drivers/mailbox/Makefile
@@ -9,3 +9,4 @@
 obj-$(CONFIG_STM32_IPCC) += stm32-ipcc.o
 obj-$(CONFIG_TEGRA_HSP) += tegra-hsp.o
 obj-$(CONFIG_K3_SEC_PROXY) += k3-sec-proxy.o
+obj-$(CONFIG_ZYNQMP_IPI) += zynqmp-ipi.o