This patch adds some endianness-agnostic helpers to convert machine
instructions between canonical integer form and in-memory
representation.

A canonical integer form for representing instructions is also
formalised here.
Signed-off-by: NDave Martin <dave.martin@linaro.org>
Acked-by: NNicolas Pitre <nico@linaro.org>
Tested-by: NJon Medhurst <tixy@yxit.co.uk>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>