[platform][vexpress-a9] initial add of platform support for arm versatile express for cortex-a9
[scripts] point do-qemuarm at vexpress-a9 instead of realview-pb
[arch][arm] add a few more cp15 accessor routines
[platform] remove realview-pb

vexpress-* is the new qemu target
[platform][vexpress-a9] add proper interrupt driven uart rx