Renamed config -> cfg

Note this includes both the lfs3_config -> lfs3_cfg structs as well as
the LFS3_CONFIG -> LFS3_CFG include define:

- LFS3_CONFIG -> LFS3_CFG
- struct lfs3_config -> struct lfs3_cfg
- struct lfs3_file_config -> struct lfs3_file_cfg
- struct lfs3_*bd_config -> struct lfs3_*bd_cfg
- cfg -> cfg

We were already using cfg as the variable name everywhere. The fact that
these names were different was an inconsistency that should be fixed
since we're committing to an API break.

LFS3_CFG is already out-of-date from upstream, and there's plans for a
config rework, but I figured I'd go ahead and change it as well to lower
the chances it gets overlooked.

---

Note this does _not_ affect LFS3_TAG_CONFIG. Having the on-disk vs
driver-level config take slightly different names is not a bad thing.

runners/test_runner.h

@@ -30,7 +30,7 @@ void test_trace(const char *fmt, ...);
 
 
 // generated test configurations
-struct lfs3_config;
+struct lfs3_cfg;
 
 enum test_flags {
     TEST_INTERNAL  = 0x1,
@@ -56,7 +56,7 @@ struct test_case {
     size_t permutations;
 
     bool (*if_)(void);
-    void (*run)(struct lfs3_config *cfg);
+    void (*run)(struct lfs3_cfg *cfg);
 };
 
 struct test_suite {