mips, net: ensure that SOCK_COREDUMP is defined

For historical reasons mips has to override the socket enum values but
the defines are all the same. So simply move the ARCH_HAS_SOCKET_TYPES
scope.

Fixes: a9194f88 ("coredump: add coredump socket")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>