buildroot

configs/qemu: update xtensa linux to 4.9

Linux configs are missing memmap= option that is required for xtfpga
boards configured w/o device tree starting with linux-4.9. Add it.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>