Fix include statements for qemu-common.h

Fix include statements for qemu-common.h

* qemu-common.h is not a system include file, so it should be included
  with "" instead of <>. Otherwise incremental builds might fail
  because only local include files are checked for changes.

* linux-user/syscall.c included the file twice.

Cc: Riku Voipio <[email protected]>
Cc: Jan Kiszka <[email protected]>
Acked-by: Kevin Wolf <[email protected]>
Signed-off-by: Stefan Weil <[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>