drivers/serial: add ram uart driver

It uses the memory block as the serial communication medium, which can communicate between different processes or different CPUs

Using the following configuration, the cross-core communication rate of 200MHz cortex-M55 is about 461KB/s
RAM_UART_BUFSIZE=1024
RAM_UART_POLLING_INTERVAL=100

Signed-off-by: yinshengkai <yinshengkai@xiaomi.com>

drivers/drivers_initialize.c

@@ -41,6 +41,7 @@
 #include <nuttx/segger/rtt.h>
 #include <nuttx/sensors/sensor.h>
 #include <nuttx/serial/pty.h>
+#include <nuttx/serial/uart_ram.h>
 #include <nuttx/syslog/syslog.h>
 #include <nuttx/syslog/syslog_console.h>
 #include <nuttx/trace.h>
@@ -118,6 +119,10 @@ void drivers_initialize(void)
   rpmsg_serialinit();
 #endif
 
+#ifdef CONFIG_RAM_UART
+  ram_serialinit();
+#endif
+
   /* Initialize the console device driver (if it is other than the standard
    * serial driver).
    */