ARM: add additional table to compressed kernel

Add an additional extendable table to the compressed kernel so that we
can provide further information to boot loaders regarding the properties
of the image contained within.

This is necessary for correct behaviour of kexec.

Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>