maixbit: workaround to avoid medium code model

targets/k210.json

@@ -1,6 +1,5 @@
 {
 	"inherits": ["riscv64"],
 	"features": ["+a", "+c", "+m", "+f", "+d"],
-	"build-tags": ["k210", "kendryte"],
-	"code-model": "medium"
+	"build-tags": ["k210", "kendryte"]
 }

targets/maixbit.ld

@@ -1,7 +1,11 @@
 
 MEMORY
 {
-    RAM (xrw) : ORIGIN = 0x80000000, LENGTH = 6M
+    /* This is a software workaround to avoid using the medany code model
+       which causes the llvm9 build to fail. 0x80000000 is mirorred at
+       0xffffffff80000000. This is not needed anymore on llvm10.
+       https://github.com/rust-embedded/riscv-rt/issues/25 */
+    RAM (xrw) : ORIGIN = 0xffffffff80000000, LENGTH = 6M
 }
 
 REGION_ALIAS("FLASH_TEXT", RAM);