include: reorganize memory API headers

Move RAMBlock functions out of ram_addr.h and cpu-common.h;
move memory API headers out of include/exec and into include/system.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

stubs/physmem.c

@@ -1,5 +1,5 @@
 #include "qemu/osdep.h"
-#include "exec/cpu-common.h"
+#include "system/ramblock.h"
 
 RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
                                    ram_addr_t *offset)

stubs/ram-block.c

@@ -1,6 +1,6 @@
 #include "qemu/osdep.h"
-#include "exec/ramlist.h"
-#include "exec/cpu-common.h"
+#include "system/ramlist.h"
+#include "system/ramblock.h"
 #include "system/memory.h"
 
 void *qemu_ram_get_host_addr(RAMBlock *rb)