greybus: Add BeaglePlay Linux Driver

Add the Greybus host driver for BeaglePlay board by BeagleBoard.org.

The current greybus setup involves running SVC in a user-space
application (GBridge) and using netlink to communicate with kernel
space. GBridge itself uses wpanusb kernel driver, so the greybus messages
travel from kernel space (gb_netlink) to user-space (GBridge) and then
back to kernel space (wpanusb) before reaching CC1352.

This driver directly communicates with CC1352 (running SVC Zephyr
application). Thus, it simplifies the complete greybus setup eliminating
user-space GBridge.

This driver is responsible for the following:
- Start SVC (CC1352) on driver load.
- Send/Receive Greybus messages to/from CC1352 using HDLC over UART.
- Print Logs from CC1352.
- Stop SVC (CC1352) on driver load.

Signed-off-by: Ayush Singh <ayushdevel1325@gmail.com>
Link: https://lore.kernel.org/r/20231017101116.178041-3-ayushdevel1325@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -8996,6 +8996,7 @@ M:	Ayush Singh <ayushdevel1325@gmail.com>
 L:	greybus-dev@lists.linaro.org (moderated for non-subscribers)
 S:	Maintained
 F:	Documentation/devicetree/bindings/net/ti,cc1352p7.yaml
+F:	drivers/greybus/gb-beagleplay.c
 
 GREYBUS SUBSYSTEM
 M:	Johan Hovold <johan@kernel.org>

drivers/greybus/Kconfig

@@ -17,6 +17,16 @@ menuconfig GREYBUS
 
 if GREYBUS
 
+config GREYBUS_BEAGLEPLAY
+	tristate "Greybus BeaglePlay driver"
+	depends on SERIAL_DEV_BUS
+	help
+	  Select this option if you have a BeaglePlay where CC1352
+	  co-processor acts as Greybus SVC.
+
+	  To compile this code as a module, chose M here: the module
+	  will be called gb-beagleplay.ko
+
 config GREYBUS_ES2
 	tristate "Greybus ES3 USB host controller"
 	depends on USB

drivers/greybus/Makefile

@@ -18,6 +18,8 @@ obj-$(CONFIG_GREYBUS)		+= greybus.o
 # needed for trace events
 ccflags-y += -I$(src)
 
+obj-$(CONFIG_GREYBUS_BEAGLEPLAY)	+= gb-beagleplay.o
+
 # Greybus Host controller drivers
 gb-es2-y := es2.o