targets,runtime,machine: add support for the stm32f469-disco board

The LEDs and button work; I haven't tested the SPI and I2C
configuration.

targets/stm32f469.ld

@@ -0,0 +1,10 @@
+
+MEMORY
+{
+    FLASH_TEXT (rw) : ORIGIN = 0x08000000, LENGTH = 2M
+    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 320K
+}
+
+_stack_size = 4K;
+
+INCLUDE "targets/arm.ld"

targets/stm32f469disco.json

@@ -0,0 +1,12 @@
+{
+  "inherits": ["cortex-m4"],
+  "build-tags": ["stm32f469disco", "stm32f469", "stm32f4", "stm32"],
+  "serial": "uart",
+  "linkerscript": "targets/stm32f469.ld",
+  "extra-files": [
+    "src/device/stm32/stm32f469.s"
+  ],
+  "flash-method": "openocd",
+  "openocd-interface": "stlink",
+  "openocd-target": "stm32f4x"
+}