cmake: Output aom_config in config sub dir.

Does away with somewhat confusing usage of "./aom_config.h" in
include statements while keeping linters silent.

aom_config.asm, aom_config.c, and aom_config.h are now written to
the config sub dir.

Change-Id: I99e2422d6ca8b20b9cdf2feee83a866c273e47b0

aom_mem/aom_mem.h

diff --git a/aom_mem/aom_mem.h b/aom_mem/aom_mem.h
index bfa460d..a36ee3e 100644
--- a/aom_mem/aom_mem.h
+++ b/aom_mem/aom_mem.h
@@ -12,8 +12,8 @@
 #ifndef AOM_MEM_AOM_MEM_H_
 #define AOM_MEM_AOM_MEM_H_
 
-#include "aom_config.h"
 #include "aom/aom_integer.h"
+#include "config/aom_config.h"
 
 #if defined(__uClinux__)
 #include <lddk.h>

aom_mem/include/aom_mem_intrnl.h

diff --git a/aom_mem/include/aom_mem_intrnl.h b/aom_mem/include/aom_mem_intrnl.h
index 3cdfbe0..977ebad 100644
--- a/aom_mem/include/aom_mem_intrnl.h
+++ b/aom_mem/include/aom_mem_intrnl.h
@@ -11,7 +11,8 @@
 
 #ifndef AOM_MEM_INCLUDE_AOM_MEM_INTRNL_H_
 #define AOM_MEM_INCLUDE_AOM_MEM_INTRNL_H_
-#include "./aom_config.h"
+
+#include "config/aom_config.h"
 
 #define ADDRESS_STORAGE_SIZE sizeof(size_t)