kernel: Set proper LD in KERNEL_KCONFIG_COMMAND

kernel: Set proper LD in KERNEL_KCONFIG_COMMAND

With 'ld-is-gold' and linux kernel 5.4 or later, menuconfig
task for kernel recipes will fail with:

$ bitbake -c menuconfig virtual/kernel
...
scripts/kconfig/mconf  Kconfig
scripts/Kconfig.include:43:  gold linker 'x86_64-poky-linux-ld' not supported
/OE/build/tmp/work-shared/qemux86-64/kernel-source/scripts/kconfig/Makefile:29:
 recipe for target 'menuconfig' failed
make[2]: *** [menuconfig] Error 1
/OE/build/tmp/work-shared/qemux86-64/kernel-source/Makefile:606:
 recipe for target 'menuconfig' failed
make[1]: *** [menuconfig] Error 2
/OE/build/tmp/work-shared/qemux86-64/kernel-source/Makefile:185:
 recipe for target '__sub-make' failed
make: *** [__sub-make] Error 2
Command failed.

This is because that the KERNEL_LD variable already set in
kernel-arch.bbclass isn't used by do_menuconfig function of
cml1.bbclass.

To fix this issue specify LD variable while calling the kernel
menuconfig command through KERNEL_KCONFIG_COMMAND.

Signed-off-by: Wonmin Jung <wonmin82@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>