mailbox: add CIX mailbox driver

The CIX mailbox controller, used in the Cix SoCs, like sky1.
facilitates message transmission between multiple processors
within the SoC, such as the AP, PM, audio DSP, SensorHub MCU,
and others.

Acked-by: Jassi Brar <jassisinghbrar@gmail.com>
Reviewed-by: Peter Chen <peter.chen@cixtech.com>
Signed-off-by: Guomin Chen <Guomin.Chen@cixtech.com>
Signed-off-by: Gary Yang <gary.yang@cixtech.com>
Signed-off-by: Lihua Liu <Lihua.Liu@cixtech.com>
Signed-off-by: Peter Chen <peter.chen@cixtech.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/mailbox/Kconfig

@@ -330,4 +330,14 @@ config THEAD_TH1520_MBOX
 	  kernel is running, and E902 core used for power management among other
 	  things.
 
+config CIX_MBOX
+        tristate "CIX Mailbox"
+        depends on ARCH_CIX || COMPILE_TEST
+        depends on OF
+        help
+          Mailbox implementation for CIX IPC system. The controller supports
+          11 mailbox channels with different operating mode and every channel
+          is unidirectional. Say Y here if you want to use the CIX Mailbox
+          support.
+
 endif

drivers/mailbox/Makefile

@@ -70,3 +70,5 @@ obj-$(CONFIG_QCOM_CPUCP_MBOX)	+= qcom-cpucp-mbox.o
 obj-$(CONFIG_QCOM_IPCC)		+= qcom-ipcc.o
 
 obj-$(CONFIG_THEAD_TH1520_MBOX)	+= mailbox-th1520.o
+
+obj-$(CONFIG_CIX_MBOX)	+= cix-mailbox.o