py/asmbase: Add MP_PLAT_COMMIT_EXEC option for handling exec code.

If a port defines MP_PLAT_COMMIT_EXEC then this function is used to turn
RAM data into executable code.  For example a port may want to write the
data to flash for execution.  The function must return a pointer to the
executable data.

py/asmbase.h

@@ -62,7 +62,11 @@ static inline size_t mp_asm_base_get_code_size(mp_asm_base_t *as) {
 }
 
 static inline void *mp_asm_base_get_code(mp_asm_base_t *as) {
+    #if defined(MP_PLAT_COMMIT_EXEC)
+    return MP_PLAT_COMMIT_EXEC(as->code_base, as->code_size);
+    #else
     return as->code_base;
+    #endif
 }
 
 #endif // MICROPY_INCLUDED_PY_ASMBASE_H