Enable the DRM backend for Weston on QEMU-x86/x86-64

The DRM backend is the native Weston backend for systems that
support the Linux kernel DRM, kernel mode setting(KMS), and evdev
input devices.

This patch set the DRM backend as default and also enable bochs
display vga interface for qemu std vga.

To use the DRM backend for Weston, the option "-vga std" should be
set into qemuparams for runqemu script, like below:

    qemuparams="-vga std"

Change-Id: I04591999a0a3f7205e42585150e8f50e7414f9ac
Signed-off-by: Tadao Tanikawa <tanikawa.tadao@jp.panasonic.com>