driver: ipm: introduce IPM_MAX_DATA_SIZE build configuration

The ipm_send() allows transferring data through the IPM device.
However, depending on the platform, the mailbox peripheral may either
transmit a limited amount of data or not transfer data at all.
Introducing this configuration allows exposing the IPM capability to the
application.
This commit defines a default value of 1024 bytes to avoid impacting
existing IPM drivers and sets the value to 0 for the STM32 IPCC and
STM32 HSEM devices.

This allows, in a next step, other devices to use this configuration to
expose their capabilities instead of using proprietary configuration or
a static definition.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

drivers/ipm/Kconfig

@@ -8,6 +8,14 @@ menuconfig IPM
 
 if IPM
 
+config IPM_MAX_DATA_SIZE
+	int "Max data size supported"
+	default 0 if IPM_STM32_IPCC || IPM_STM32_HSEM
+	default 1024
+	help
+	  Define the max size (in bytes) of data that can be transmitted or
+	  received by the IPM device.
+
 config IPM_MHU
 	bool "IPM MHU driver"
 	default y