target: reflect the fact that we're a static binary

A firmware blob is an _extermely_ static binary, and our `target.json`
settings should reflect this. It also saves us some code size to use a
"static" relocation model.

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

target.json

@@ -12,6 +12,9 @@
   "panic-strategy": "abort",
   "disable-redzone": true,
   "features": "-mmx,-sse,+soft-float",
+  "dynamic-linking-available": false,
+  "code-model": "small",
+  "relocation-model": "static",
   "pre-link-args": {
     "ld.lld": [
       "-s",