ARM: 7511/1: opcodes: Opcode definitions for the Virtualization Extensions

For now, this patch just adds a definition for the HVC instruction.
More can be added here later, as needed.

Now that we have a real example of how to use the opcode injection
macros properly, this patch also adds a cross-reference from the
explanation in opcodes.h (since without an example, figuring out
how to use the macros is not that easy).

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>