feat(machine/stm32): add STM32H7 and NUCLEO-H753ZI support

targets/stm32h7.ld

@@ -0,0 +1,19 @@
+
+MEMORY
+{
+    FLASH_TEXT (rx) : ORIGIN = 0x08000000, LENGTH = 2048K
+    RAM (xrw)       : ORIGIN = 0x24000000, LENGTH = 512K
+}
+
+/*
+ * D2 SRAM (0x30000000, 288K on H753) and D3 SRAM (0x38000000, 64K) are not
+ * mapped here and unused by the runtime. If a future driver places DMA
+ * buffers there, add MPU regions for them in initMPU()
+ * (src/runtime/runtime_stm32h7_mpu.go) — they currently fall through to the
+ * default privileged WBWA map, so cache maintenance via DCacheClean/
+ * DCacheInvalidate/DCacheFlush would silently miss those addresses.
+ */
+
+_stack_size = 8K;
+
+INCLUDE "targets/arm.ld"