kvm tools, vesa: Use guest-mapped memory for framebuffer

kvm tools, vesa: Use guest-mapped memory for framebuffer

This patch converts hw/vesa.c to use guest-mapped memory for framebuffer and
drops the slow MMIO emulation. This speeds up framebuffer accesses
considerably. Please note that this can be optimized even more with the
KVM_GET_DIRTY_LOG ioctl() as explained by Alexander Graf.

Cc: Alexander Graf <agraf@suse.de>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: John Floren <john@jfloren.net>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>