MIPS: configs: lb60: Fix defconfig not selecting correct board

Since INGENIC_GENERIC_BOARD was introduced, the JZ4740_QI_LB60 option
is no longer the default, so the symbol has to be selected by the
defconfig, otherwise the kernel built will be for a generic Ingenic
board and won't have the Device Tree blob built-in.

Cc: stable@vger.kernel.org # v5.7
Fixes: 62249209 ("MIPS: ingenic: Default to a generic board")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>