qemu/arm-vexpress: add new sample config

By popular demand!

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

board/qemu/arm-vexpress/readme.txt

@@ -0,0 +1,6 @@
+Run the emulation with:
+
+  qemu-system-arm -M vexpress-a9 -kernel output/images/zImage -drive file=output/images/rootfs.ext2,if=sd -append "console=ttyAMA0,115200 root=/dev/mmcblk0" -serial stdio -net nic,model=lan9118 -net user
+
+The login prompt will appear in the terminal that started Qemu. The
+graphical window is the framebuffer.

configs/qemu_arm_vexpress_defconfig

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+# Architecture
+BR2_arm=y
+BR2_cortex_a9=y
+
+# system
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
+BR2_TARGET_GENERIC_GETTY=y
+BR2_TARGET_GENERIC_GETTY_PORT="ttyAMA0"
+
+# filesystem
+BR2_TARGET_ROOTFS_EXT2=y
+# BR2_TARGET_ROOTFS_TAR is not set
+
+# Lock to 3.3 headers to avoid breaking with newer kernels
+BR2_KERNEL_HEADERS_3_3=y
+
+# Kernel
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="3.3.4"
+BR2_LINUX_KERNEL_DEFCONFIG="vexpress"
+BR2_LINUX_KERNEL_ZIMAGE=y