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: [e-mail] # v5.7
Fixes: 62249209a772 ("MIPS: ingenic: Default to a generic board")
Signed-off-by: Paul Cercueil <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/configs/qi_lb60_defconfig

···
 # CONFIG_COMPAT_BRK is not set
 CONFIG_SLAB=y
 CONFIG_MACH_INGENIC=y
+CONFIG_JZ4740_QI_LB60=y
 CONFIG_HZ_100=y
 # CONFIG_SECCOMP is not set
 CONFIG_MODULES=y