firmware: zynqmp: Add zynqmp-power support

zynqmp-power driver for ZynqMP to handle the communication with the PMU
firmware. Firmware driver just probes subnodes and power driver handles
communication with PMU using the IPI mailbox driver.

Signed-off-by: Ibai Erkiaga <ibai.erkiaga-elorza@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 257a98d..0c41bc3 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1051,6 +1051,7 @@
 	select CLK
 	select DM
 	select DM_ETH if NET
+	select DM_MAILBOX
 	select DM_MMC if MMC
 	select DM_SERIAL
 	select DM_SPI if SPI
@@ -1061,6 +1062,7 @@
 	select SPL_CLK if SPL
 	select SPL_SEPARATE_BSS if SPL
 	select SUPPORT_SPL
+	select ZYNQMP_IPI
 	imply BOARD_LATE_INIT
 	imply CMD_DM
 	imply FAT_WRITE