kvm tools, bios: Fix BIOS to kernel memory copy

This patch implements memcpy16() function that copies memory areas in 16-bit
real mode and converts bios/int10.c to use it instead of relying on GCC struct
memcpy to do the right thing.

Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Asias He <asias.hejun@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>